I'm having the same symptoms as described here, except many times it will happen during login just after I enter my username/password and press enter. Whether I make it past the login and into the game or not, the problem is the same: no keyboard commands do anything and mouse only moves around on the screen. The game is completely hung and I am unable to give any command that will get the system out of the state other than resbooting. I haven't been able to try logging into my system remotely in order to kill processes, but I wouldnt' be surprised if that works.
I think this is a matter of the keyboard and mouse events all being captured by the game, and the game being in a state where it cannot handle the events. I'll post with more info when I'm able to test out killing the needed processes via remote login.
I know this issue is not related to overheating, but I can't rule out the possibility of it being related to my graphics driver. Here's my system info:
Hardware:
Processor: Intel Core 2 Duo T9400 @ 2.53GHz (2 Cores), Motherboard: LENOVO 4061BL2, Chipset: Intel Mobile 4 MCH + ICH9M-E, Memory: 8192MB, Disk: 160GB HITACHI HTS72321, Graphics: ATI Mobility Radeon HD 3650 512MB, Audio: Conexant CX20561 (Hermosa), Network: Intel 82567LM Gigabit Connection + Intel PRO/Wireless
Software:
OS: Ubuntu 12.04, Kernel: 3.2.0-25-generic (x86_64), Desktop: Unity 2D, Display Server: X Server 1.11.3, Display Driver: fglrx 8.96.4, OpenGL: 3.3.11627, Compiler: GCC 4.6, File-System: ext4, Screen Resolution: 1920x1200