I was testing Roll20 last night with two of my players, and we were mostly really pleased with how smooth it all went. Only a couple things came up. One was player editing permissions on tokens, which is discussed elsewhere and I've voted to +1 those posts.
The other was the ability, if possible, to have the size of the video display windows alter based on the broadcast settings of the particular client (basically, if you're only broadcasting or only receiving audio, then the camera window doesn't need to be there, and a smaller window - maybe with just a small silhouette icon and a speaker icon - is all that's needed).
Trying to determine this automatically might get weird since each player can decide whether to transmit and receive differently, but a button in the screen to toggle it from big to small would be ample. Since none of us have cameras, the camera screen was essentially wasted space. Not a big deal, but something to consider.
Here's a mockup complete with smaller video screens, and even a crappy "expand me" icon.
