Valve announced today that its Steam digital distribution system has exceeded 15 million users, a feat that is most definitely worthy of cake.

In addition, an official press release states that Valve has seen 158% sales growth over the last holiday season, putting the company in a pretty good place coming into 2008. Steam's rapid growth is likely due in part to the critical success of Portal, as well as the ever-expanding offerings available through the download service.

Full story: joystiq.com