I had this problem last night. I don't have access to the computer we used, but I'll describe a well as I can.
We use Roll20 for playing around a table with a TV built in the center. We use two computers, one for the DM and one for the players. The screen receives video from the Player PC. Both computers are windows 7, asus laptops with Chrome. Playing dnd 4e
The Problems:
1) On DM PC, I would have to move the player after updating health/auras/status balls(is that what they're called?) before I could see the update. This was a bit annoying, but not so bad. They would hide themselves again from time to time and I would just move the token to get it to show back up.
2) It was very confusing on what the Player PC could edit. I wanted the Player PC to be able to change the health bars and auras of the Player tokens, but I kept having to make the same changes on the DM PC to match what the Player PC had done. However, there were a few cases where the Player PC would update a token's life, and I would see it on the DM PC.
3) My DM controlled tokens were lacking all graphics. I couldn't get them to see health bars or auras or status balls that I put on my enemy tokens. We use an aura of radius 1 and color red to indicate bloodied so this is very important.
4) When I (DM PC) updated the position of an object on the map, it seemed to lag for set amount of time for different objects. For example, I used a compass display and every time I move it, it would take minutes for the location to update on the Player PC. We didn't have this problem for the player tokens. Well, maybe once or twice throughout the night for player tokens.
That's all I can think of right now, and I'll be happy to post specifics and maybe try to get some screen shots later tonight if you think it will help.