I snuck a couple of photos of the two main exhibition rooms with my phone cam.
This first pic is of the main events room and was taken right after closing ceremonies. Capacity is about 3500; it was about 1/2 - 2/3 full during the AMV show. The pic doesn't give a good view of how long the room is. In the center is the main screen; it's 20-30 feet across. It's flanked by two screens, and there are two smaller ones that hang from the ceiling about halfway to the back wall which is where this pic was taken.
This next pic is of the auxiliary events room which is where AMV Hell 3 was shown (followed by three more hours of AMVs and hosted by Vlad). I think we figured it could hold about 350 people. I know it was not full when AMV Hell was running (maybe 150-200). The picture was taken during the charity auction.
The AMV panel and the first AMV 4-hour block were held in a smaller room on Friday. And, someone was running a 24/7 AMV room elsewhere in the convention center. It was not quite as large as the aux room, but there were always many people there every time I looked in.