We get quite some people asking this everyday. When will GNOME 2.12 appear in Debian? Not yet? Why don't you upload to alioth?
For a few months we've been holding all kind of GNOME uploads unless they were absolutely necessary, to try to get GNOME 2.10 in etch. This has been a hard battle due to the unusual number of ongoing transitions in Debian at the time: glibc, gcc-4.0 as default compiler, C++ abi, XFree86 -> X.Org. At first we thought we'd be able to by-pass most of them by not uploading anything but in the end control-center got stuck behind X.Org, and that complicated things quite a bit.
Luckily, the Release Team, with help from the glibc and X maintainers, have managed to get these in testing after getting rid of the RC bugs caused by the new versions, opening the door for GNOME 2.10, which was able to enter testing (unblocking the testing transition for some 150 additional packages) coincidentally a few days after the GNOME 2.12 release. Oh well, these things happen when you want a Debian release out every half decade or so. :) We owe Loïc Minier quite some beers, because he has been tracking problems with GNOME 2.10 for a few months, and has suddenly become one of the key members in the team!
So, with GNOME 2.10 in testing, our current plan to bring GNOME 2.12 to Debian is:
Finish up GNOME 2.10
To avoid making the transition even more complicated, we held any new 2.10 uploads to unstable for over two months. In that time, some GNOME components released new versions, and will now be updated so etch has a completely stable GNOME 2.10 suite. This step is ongoing and should be easy to complete, unless the long list of Mozilla RC bugs holds it for a while.
GNOME 2.12 to experimental
With GNOME 2.10 safe in etch, we'll be able to focus our attention to GNOME 2.12. Some modules have been branched for experimental already, and soon you'll be able to find more and more in there. While doing experimental 2.12, our plan is to completely transition our gconf setup to install defaults in /var instead of /etc, plus start handling the update of icon caches when necessary. These transitions shouldn't be too complicated. There's another transition that will hit 2.12, though; hal/dbus 0.50 which may get a bit more complicated because it affects packages outside the Debian GNOME Team's influence (Qt/KDE being an example). We'll see how that one goes.
GNOME 2.12 to unstable
By the time we're ready to do an experimental upload, hopefully the rest of testing transitions will have been cleared up, and having GNOME 2.12 in unstable and then testing should be pretty easy. Or that's my hope. :)
Be prepared to see more and more 2.12 fun in experimental in some days. When more or less is in place, we'll upload a 2.12 meta-package suit, so it'll be easy to upgrade in just one command. For now, you'll have to ask Google about how to deal with GNOME in experimental.