I'm a new linux user and I downloaded this program first on Linux Mint 13 64-bit Cinnamon. It worked fine until I started Steam. The system then got progressively slower until becoming completely unresponsive. I've been able to reproduce this bug numerous times. When I switched to Kubuntu 13.04 I was able to reproduce the bug once again.
I don't have a weak system. I'm running two Radeon HD 5850s in crossfire with a Core i7-920 @ stock 2.66GHz, hyperthreading enabled. I'm currently running Kubuntu 13.04 64-bit with the same results. I tried disabling crossfire and it seemed to work a little while longer but shortly started to freeze my system again.