I've just upgraded to oneiric and a few seconds after logging into unity 3D, the whole desktop freezes. I tried unity --reset, unity --advanced-debugging, re-enable from the ccsm. The only thing I could do is restart lightdm from a tty and log in to unity 2D but it is too slow. My machine passes the unity support test. The interesting part is that the beta2 release worked just fine. I would file a bug, but I can't decide whether it's a unity/gtk3/compiz bug. -Has anyone met this issue before? -Is there any way I could use Unity 3D somehow, bypassing the issue? -What should I do to help debug this one?
I had the same issue (described in bug #728745) and I successfully solved it after activating the nvidia-173-updates driver in the additional drivers preferences (as suggested in this comment). It is said to disable hibernation and multiple screens.
Note that a newer driver version is mentioned in the bug thread (version 275.43, see comments #144 and #145) that is said to fix everything, but I was reluctant to try it, because it has to be installed manually (you have to disable Nouvau, exit X and run it from a terminal) and in the future updated manually (through the nvidia-installer program) and who knows how this might play with future Ubuntu updates. Anyway, 173 works fine for me for now, so if it ain't broken, don't fix it :)