Steam has something in beta right now (the name escapes me) where you can essentiall share your games with ANYONE with a steam account.
So....let's say I have the Batman game I was just referring to....and my roommate wants to try it. I send an "invite" to his account name, and then he can install it too. lol
It seems so ridiculous to think about, but it's incredible how progressive that company is. My roommate has like 200 games on his account, so it'd benefit memorethan him =P
Oderint Dum Metuant