Running Intel Core 2 Quad x64 ubuntu precise 12.04 Dell OptiPlex 760 nvidia graphics driver
Unfortunately I uninstalled Ubuntu... Just couldn't deal with the incompatibilities and issues and I needed to start being productive again... back to Windows 7 for me. :-\
So it sounds like this issue can be caused by a variety of different things and no 1 single answer is correct. Too localized?