[james4k]

Officially, they are flexible on the actual rate, but I believe 30% is pretty standard.

http://www.forbes.com/forbes/2011/0228/technology-gabe-newel...

Edit: Oh, and PC Gamer has a good bit about the update process.

http://www.pcgamer.com/2012/07/12/how-steam-is-about-to-chan...