I was surprised to find out that mine is no less than 49 Gigs, which means it's covering one third of my C partition. I figure that's due to the three parallel Empires installations. How big are your respective Valve folders, and what's in them? EDIT: If somebody brings an Over 9000 joke I will instantly apply for a moderator position, just so I can ban you personally.
Keep in mind that SVN folders have the tendency to report a file size larger than what it really is, so there isn't as much in there as you'd think.
Haha a mere 13.4GB...I feel inadequate next to you guys. Mind you thats only: Empires Left 4 Dead Audiosurf, hardly disk eating games. Only other game I have installed is Sins of a Solar Empire