Quick Ubuntu / Ubuntu GNOME 14.10 Utopic Unicorn update: GNOME Shell 3.12 and GTK+ 3.12 have recently landed in the official Utopic repositories.
Currently, GTK+ 3.12 is available in the proposed repositories, so if you're already using Utopic, you'll have to wait a bit for the package to be available in main or you can enable the proposed repositories.
Unfortunately, GNOME Shell and GTK+ 3.12 are pretty much the only GNOME 3.12 packages available in the Utopic repositories (with maybe a few non-default exceptions like GNOME Music), at least for now. Nautilus, Gedit, Totem and so on are still at version 3.10 and GNOME Control Center and GNOME Settings Daemon at 3.8.6, but it's still very early in the Ubuntu 14.10 Utopic Unicorn development stages (the first alpha for opt-in flavors will be released on June 26th), so there is still time for these to be updated.
It's also important to note that Ubuntu / Ubuntu GNOME 14.10 most likely won't ship with GNOME 3.14. That's because GNOME 3.14 is released on September 25th while the final Ubuntu 14.10 release is on October 23rd and there's not enough time to get everything ready/tested until then (especially considering that Ubuntu ships with some GNOME apps that need quite a few patches to work/look properly under Unity).
It's also important to note that Ubuntu / Ubuntu GNOME 14.10 most likely won't ship with GNOME 3.14. That's because GNOME 3.14 is released on September 25th while the final Ubuntu 14.10 release is on October 23rd and there's not enough time to get everything ready/tested until then (especially considering that Ubuntu ships with some GNOME apps that need quite a few patches to work/look properly under Unity).
