I'm a big fan of the Personal Democracy Forum's archive of conference calls and would say that you'll get value out of listening to any of them. They're usually around 45-60 minutes long, with a heavy hitter from one of the online platforms speaking about the uses of their technology, followed by a Q&A with the conference call attendees.
Of particular interest to me were the ones on Ning and Youtube. So far I've only listened to around 5-6 of these, but over the next few months I'll be making time for as many as I can. If any particularly good ones crop up I'll make sure to share.