For me social media is about the conversation. The ability to communicate, share and collaborate without the constraints of time and geography.
From a learning perspective the wealth of curated information, content and links I get through social media means that learning stops been about finding stuff and becomes about using stuff.
Social media is not about reading everything, it is about dipping into the stream of ideas, content and information as it passes you by.
Reminded of this article I wrote on my blog http://elearningstuff.net/2008/12/05/its-all-about-the-coffee/ how Twitter (and thus other social media) is about the coffee, well the conversations we have over coffee.