I just got through listening to CC Chapman's latest installment of Managing the Gray, where CC gives a great primer on SL.  It's a fantastic summary of what SL is and isn't.

If you've heard the buzz about SL but still don't have any idea what it's all about, check out this podcast.   When people ask me about SL, I'm sending them a link to this podcast.

Also, if you're into social media check out the rest of his podcasts, he's a succesful guy who has a lot to say. 

I'm listening and learning.