Comment 205 for bug 973096

Looks like this problem is infecting OS X too.

"These suggest the problem is likely a driver fault; however, it could also be a bug in the Window Server that occurs when performing certain actions that used advanced graphics capabilities."
http://reviews.cnet.com/8301-13727_7-57485204-263/mac-pro-users-experiencing-random-log-outs-in-mountain-lion/

 Sounds almost exactly what has been described here. Driver or X server?