When you say you are running 12.04 classic, do you mean: (1) Ubuntu 12.04 with Unity or (2) Ubuntu with GNOME and launching GNOME Classic?
I am going to go with (2).
GNOME Classic is not 100% the same as the original GNOME that was found in Ubuntu 10.04. It is provided as a temporary solution, but long term support for it is doubtful. You can read more here (GNOME Classic is the same as GNOME Fallback). Any tweeks you see on other sites are to get the GNOME Fallback to look “reasonably” like GNOME 2, but they are never quite 100% (at least I have never seen any tweeks that make GNOME Fallback 100% the same as the original GNOME 2).
If you want a true GNOME 2 experience (the same as in Ubuntu 10.04), then I suggest installing the MATE Desktop. MATE is a fork (independent development from GNOME) that maintains the original GNOME 2 desktop.
I hope this answers your question and thanks for asking.

Ok, I think I finally understand what your original question was (I was thinking about the look and feel and not clueing in at all on the GNOME 3D thing) – that’s why I pointed to ubuntu-artwork.
I run Ubuntu as a guest in VirtualBox running on Windows 7 and, after your last comment, I was able to reproduce exactly what you describe (unless, I am misunderstanding you again).
If I install GNOME, I don’t get the GNOME 3D effects – even if I enable 3D acceleration. I also noticed the VirtualBox Guest Additions were not building – this requires the following:
(1) check your kernel version:
uname -r
for me it spit back 3.2.0-23-generic-pae – we need this.
(2) enter the following commands:
sudo apt-get update
sudo apt-get install make
sudo apt-get install linux-headers-3.2.0-23-generic-pae
The string you got back in step (1) is appended to linux-headers-. We have to install make because, for some reason, while gcc got installed, make did not.
If you installed gnome-shell instead of gnome, then you will also have to install gnome-terminal and gcc.
(3) install the VirtualBox Guest Additions
(4) shut down the machine
(5) enable 3D acceleration on the VirtualBox machine
(6) start the machine up again
It should now work with GNOME 3D.
[if you – or anyone else – replies to this comment, I prefer a new comment thread be started because I have discovered that WordPress limits nested comments to a maximum of 10 levels]

Thanks again, but as I mentioned, openSUSE had no problem picking up the hardware and running Gnome3 with Shell. As well, Ubuntu Desktop edition installed just fine and ran Unity3D. I can’t see how this would be the issue. I’m going to rest on something in the repos about the version of Gnome is not right. I haven’t had time yet to try the gnome3-team PPA, but will report back the results when I do. Last resort would be to build it and see what happens.

The only reason I can think of is that GNOME thinks you don’t have 3D hardware support and is downgrading itself. You mention running a VM, perhaps you need to enable 3D acceleration and bump up the video memory. As well, you may need to install some virtual machine specific drivers (I am thinking of VirtualBoxes Guest Additions).
You can read about the decision to merge the two cores . Basically, the differences between the two used to be the tasking model – now they use the same tasking model. Basically, this means (perhaps) slightly lower performance for some applications since tasking overhead is a little higher than it might have been for the server.
On the other hand, it makes life easier for Ubuntu since they only need to test and maintain one kernel instead of two.

admin, thanks for all that feedback.
Yes, I am aware Gnome Classic is really Gnome3 under the hood.
What I don’t understand is that why when I choose Gnome in the login menu, I get Gnome Classic instead. It seems I cannot get Gnome shell no matter what I do. Hardware support isn’t an issue as I mentioned – I’ve already managed to install openSUSE in a VM and it used Gnome-Shell just fine.
I’ll check out those other packages for Ubuntu styling and branding. I think that is definitely what I was looking for, I just didn’t know the package names and I didn’t want to have to install full blown unity just to get them. Thanks for the tip.
I guess now I’ll have to try with a fresh copy of this server VM and see what I can manage to get working. (I’ll skip gnome-session-fallback this time and see if only installing gnome or gnome-shell actually gets me Gnome Shell.)
After some research, it seems I may be able to simply install the desktop .iso afterall. Previously with 10.04, I installed the server version and then added ubuntu-desktop. This is because for whatever reason, I got better performance overall and in some specific use cases for a normal workstation with the server kernel than with the desktop one. Now that the two kernels have been merged into one, I guess that reason no longer exists. Though it begs the question, did we all end up with the server kernel, or did servers end up with a desktop kernel or is the result some hybrid of the two? I’ve never seen any list of what the differences were with Precise vs. earlier versions.
Anyway, that’s neither here no there concerning gui’s.
Off to installing it is then…

Thanks for all your clarifications. I wasn’t sure if you were someone who had installed Ubuntu Server by accident and were trying to get GNOME Desktop on it.
GNOME Classic is really GNOME 3 underneath, it is just styled to look like GNOME 2 (more or less). The only existing GNOME 2 project (that I am aware of) is MATE.
If you want that Ubuntu look, you will need to install ubuntu-artwork.
Here are my (next) tentative install instructions:
sudo apt-get install gnome-shell
sudo apt-get install lightdm-gtk-greeter
sudo apt-get install ubuntu-artwork
gnome-shell pulls in some apps (Nautilus file manger, brasero disc burner, system settings and a few others).
lightdm-gtk-greeter doesn’t look like the Ubuntu login screen (that’s unity-greeter), but it is the lightest of the login screens (I did discover that if you install a greeter / login screen without installing a Window Manager and reboot, you can’t get to a command line from the login. sigh.)
ubuntu-artwork pulls in all the necessary wallpapers, background, fonts, widgets, etc to make the desktop look (more or less) like Ubuntu
Now to refine this to come up with the tightest GNOME 3 install and the tightest any GUI install.
I believe the disk usage for this install is (I did have lxde-core installed as well, so it may have pulled in some files not reflected in these numbers):
gnome-shell : 334 MB
lightdm-gtk-greeter : 29.5 MB
ubuntu-artwork : 27.9 MB
It still seems unnecessarily large to me – mind you xserver-xorg weighs in at 65.1 MB (237 MB with suggested packages).
[UPDATE 06-June-2012 @ 08:03]
Installing
gnome-shell + lightdm-gtk-greeter + ubuntu-artwork = 484 MB
gnome-shell + unity-greeter + ubuntu-artwork = 485 MB
I think it makes sense to go with the unity-greeter instead – makes everything look more uniform.
lxde-core + lightdm-gtk-greeter = 159 MB
lxde-core + unity-greeter = 365 MB
Other windowing managers with lightdm-gtk-greeter:
fluxbox : 93 MB
blackbox : 84.3 MB
compiz : 110 MB
metacity : 471 MB
lxde : 197 MB
xfce4 : 213 MB
mutter : 480 MB
matchbox : 93.6 MB
openbox : 101 MB
awesome : 102 MB

ok, just as long as you were aware that purge or remove doesn’t usually remove all package contents and dependencies.

Hi admin,
That is exactly what I wanted. purge unity would remove only unity, but will keep notification applets, icons, wallpapers, ambience theme, etc. which comes installed with it. Missing these was the problem of SamAdams, if I understand correctly.

The problem is that remove, purge don’t work as you woould expect them. I have extensive write-ups on apt-get remove here and here.
Consider the following apt-get session to install lxde-core:
richard@richard-VirtualBox:~$ sudo apt-get install lxde-core
Reading package lists... Done
Building dependency tree
Reading state information... Done
The following extra packages will be installed:
libfm-data libfm-gtk-data libfm-gtk1 libfm1 libid3tag0 libimlib2
libjpeg-progs libjpeg-turbo-progs libmenu-cache1 libobrender27 libobt0
lxde-common lxmenu-data lxpanel lxsession lxshortcut obconf openbox
openbox-themes pcmanfm xscreensaver xscreensaver-data
Suggested packages:
lxlauncher gpicview ttf-dejavu libxml2-dev xfishtank xdaliclock
xscreensaver-gl fortune qcam streamer gdm3 kdm-gdmcompat
The following NEW packages will be installed:
libfm-data libfm-gtk-data libfm-gtk1 libfm1 libid3tag0 libimlib2
libjpeg-progs libjpeg-turbo-progs libmenu-cache1 libobrender27 libobt0
lxde-common lxde-core lxmenu-data lxpanel lxsession lxshortcut obconf
openbox openbox-themes pcmanfm xscreensaver xscreensaver-data
0 upgraded, 23 newly installed, 0 to remove and 275 not upgraded.
Need to get 3,636 kB of archives.
After this operation, 19.5 MB of additional disk space will be used.
Do you want to continue [Y/n]? y
You can see that it installs 23 packages and uses 19.5 MB of disk space.
The corresponding apt-get session using purge (or remove) along with --auto-purge is:
richard@richard-VirtualBox:~$ sudo apt-get purge --auto-remove lxde-core
Reading package lists... Done
Building dependency tree
Reading state information... Done
The following packages will be REMOVED:
lxde-core*
0 upgraded, 0 newly installed, 1 to remove and 275 not upgraded.
After this operation, 36.9 kB disk space will be freed.
Do you want to continue [Y/n]?
As you can see, it only removes 1 package and frees up only 36.9 kB of disk space.
Thanks for your comments, it encourages me that people follow my website and wish to engage actively here – that is one of the reasons I allow comments (the other being that I want feedback as well).

The easiest way would be:
sudo apt-get install ubuntu-desktop
sudo apt-get purge unity unity2d
sudo apt-get install gnome
sudo apt-get autoremove