How do social media change the conversation?

Time Magazine's cover story this week is about Twitter - it's by Stephen Johnson, and it's a good intro to how users of social media are extending its reach and transforming traditional conferencing and dialog formats. E.g.:

Injecting Twitter into that conversation fundamentally changed the rules of engagement. It added a second layer of discussion and brought a wider audience into what would have been a private exchange. And it gave the event an afterlife on the Web. Yes, it was built entirely out of 140-character messages, but the sum total of those tweets added up to something truly substantive, like a suspension bridge made of pebbles. more here.