Most consumer firewalls won't block it, but most corporate ones will. Eventually we'll implement a server-based fall-back, but that would suck in a few ways.

Edit: That's really surprising that your voice and video are getting cut up. It usually either works very well or just doesn't (if it's a firewall issue). thorax, can you email zhyder AT dabbleboard DOT com?

As for the desktop sharing, we'll be releasing the feature to allow you to choose which rectangular region to share. But we probably won't have the ability to select specific applications to share though; limitation of a browser-based solution.