I didn't find anything in search. Now, I'm on LiveCD, but I think, that after installation, I'll have the same problem. My Mint version is 12.
Instead of Gnome 3, I have a strange graphical environment that looks like Gnome 2 or Xfce. I guess that's MATE.
My question is: why I can't start a Gnome 3 session? On Fedora, Gnome 3 works fine :O