GNOME 2.12 is mostly in experimental now (for i386, builds for powerpc are very welcome), only missing a control center and gnome-panel upload, plus gal being ACCEPTed so evolution 2.4 can be installed.
Trying these packages is easy: on an up to date unstable system, just issue:
apt-get install -t experimental gnome-desktop-environment
Due to a dbus transition, you might get some packages removed if they don't have an experimental build using the new versions. In many cases, there's nothing we can do about it so it's a matter of waiting.
The good news is that KDE has finally entered testing, so I'd expect that we'll be able to upload all of these packages to unstable quite soon. Hopefully before April, when GNOME 2.14 is due. :)
Update: By the way, in case you're still cursing about that major evolution breakage the other day... yes, it was totally me to blame. :)