I'm impressed with Jitsi, it all works pretty well. The only thing i noticed, compared to some of the proprietary solutions, is that my laptop got pretty hot because of CPU usage. I wonder if they're doing anything about that for the next release.
Jitsi simply forwards the video streams between users, whereas some proprietary services seem to re-encode everything into a single stream. So in a large conference each client might have to deal with decoding dozens of high-resolution streams. This is probably very difficult to solve without reducing video quality.
