This is a game changer, you guys.
Steam just released information that starting next week, they will be opening up a beta for a feature allowing you to share your digital game library with close friends and family, with achievements and saves being logged to each individual account. Basically, you give authorization to a friend's computer to access your library, and they can play your games with no problems. There are limitations- you can only authorize ten devices (they don't say if you can rescind permission; maybe that's coming), and you share the ENTIRE library at one time. That means that if a friend of yours is using your library, you cannot also use your library at the same time. Additionally, not all games will be available on the share, due to technical difficulties with some of them (some games need 3rd party keys, etc.)
Still, I think that this is super rad. I've wanted for ages to be able to share some of my games with others (EVERYONE MUST PLAY BIOSHOCK INFINITE). I also kind of love that Steam is doing this-- so many other companies are freaking out about sharing rights to things because then maybe people won't buy their stuff, and Steam is just like "we DGAF. Hats." I wonder if this will actually lead to a rise in sales for Steam (if the owner of the Steam library opens up their library while you are playing a game you lose access, with a box that pops up offering to allow you to buy the game you were playing).
(more info: http://store.steampowered.com/sharing/