During the holiday season alone, Steam reported 5 million simultaneous gamers online.
For those that enjoy hardware, and we know there are a lot of you on our site, here's a fun stat for you: Steam served 780 Petabytes -- that's 817,889,280 Gigabytes -- worldwide in 2011 alone. Unfathomable, we know. Can you imagine having ONE BILLION gigs of hard drive space?
Valve is moving to accommodate its growing demand with solidified network architecture to continue offering its (relatively) fast download service.