FaceBook: Same as above.
Second Life: This is a GAME. I don't get why people think it's more than that. The only thing that sets it apart from other MMOs is that it's a really bad game. Calling it a "social networking entity" is pure spin. It boasts millions of "registered" users, but what they gloss over is that only a handful of people actually consistently "play". Of course they'd be able to claim an outlandish number of users since it's free to register and download the client. But if one actually wanted to do anything substantial in the game world, the user would have to fork over real money. So, no...I don't see any value in exploring Second Life as an avenue to expose new people to the library...especially given that only a few people actaully play the game. If the library really wanted to tap the deep waters of MMO subscribers, they'd be better off building "Library Island" in WoW.