http://www.pokerstars.com/poker/room/features/security/
An excerpt:
"To ensure this and avoid major problems described in [2], we are using two independent sources of truly random data:
- user input, including summary of mouse movements and events timing, collected from client software
- true hardware random number generator developed by Intel [3], which uses thermal noise as an entropy source"
After looking at this thread I remembered that many months ago I read something on the Poker Stars website which made me feel more secure about their online poker room.