For me, Twitter has been invaluable in not only finding resources that I can digest on my own time, but also live, "in-the-moment" professional development. There have been countless times that I've contributed to workshops or parent nights in places that I may never physically see.
Some of the Twittering-conference experiences I've had have been much more meaningful than actual events I've been to. Part of it has to do with the fact that the folks you are going to find taking part in professional development via Tweets and backchannels are the totally obsessive types who really love what they do and love to talk about teaching and technology.
They are more akin to insane record collectors at a vinyl conference than to (no offense, but honestly) the typical required-prof-development ed conference crowd. In short: if someone is taking the time to take part in a conference via Twitter, then they probably REALLY WANT TO BE THERE. As in: given the choice between going to the ed conference and doing ANYTHING ELSE, they'd choose the ed conference.