I randomly have mouse/unity/system hang-ups since the upgrade to 11.10. I did't have any issues with 11.04 though.
The mouse just freezes and the system is no longer responsive at all. No keystrokes are possible or any other interaction but to reset the system. The system doesn't seem to crash, it just freezes. There are no usable log informations available as far as I can tell.
This happend after a upgrade from 11.04 to 11.10 and on the installation process with the amd64 media on a fresh install.
Using the fglrx. The situation is the same with unity 2D.
Hardware: Sapphire Radeon HD6850 Intel Classic DP43BF