1. Not really, but it's endlessly entertaining and sometimes even useful. I haven't made any meaningful new connections though recently I got accidentally friended by a private equity guy who gave me a little advice for my companies. The only issue I've seen come up repeatedly is when relationship breakups hit the mini-feed with the little broken heart icon. The real-timeness of this is a bit much for some people.

2. I tried Joost a while ago and there wasn't much that seemed worth watching. Usually I browse http://www.videosift.com which is a digg like site for online video. It's mostly limited to short clips and a few longer videos that no one reports to Google for deletion. Joox.net is also outright amazing but you need to install a plugin (seamless install in Firefox)

3. As the community gets bigger news has to start appealing to the lowest common denominator. see http://news.ycombinator.com/item?id=40284