<audio> and <video> pretty much work fine AFAIK. We're now talking about putting a P2P/VoIP/videoconferencing stack into the browser which is a bit more complex.

I still can't put <video src=blah></video> in a page and expect it to work in every browser. I need at least webm + mp4, or ogv + mp4, so I double the space utilization on my server for every video maintaining redundant copies, in addition to the various resolutions you make video at because ISPs are assholes and we are still in the dark ages of internet speeds.

A problem exists, because there's no standard way to access microphone and camera. And this access is absolutely essential in order to implement voip. Hence, we've got flash, which is becoming a big problem, because it's been discontinued on some platforms.