gonme 3.2 is available in testing now so switch your repos to the testing ones
Not quite ready in testing yet. (Getting there)
If you switch to testing a do a full DU. You will have Gnome 3.0 (with Shell and fallback mode).
Gnome 3.0 can not use Mint MSGE extensions (3.2only). But runs nicely with 3.0 extensions and themes.
Gnome 3.2 is not fully updated in SID as yet either.http://www.0d.be/debian/debian-gnome-3.2-status.html
You may have to add some packages from experimental to have a full Gnome 3.2.
Probably be another few weeks to a month before 3.2 is in testing.