You can get all of the entries and results from Masters Nationals at
http://www.racetrak.com/regatta.asp?CurrRegattaID=190. I think the doubles were probably the largest event here as well, although entries were probably in the twenties rather than the forties. There were events ranging from AA through J, some with several heats, some with finals only and just two or three entrants. In general I'd say B, C and D probably had the most entries overall. Each competitor was limited to 6 events.
The course in Oak Ridge is fantastic. Very nicely laid out, easy to get on and off the docks, plenty of room heading up to the start. As luck would have it, Oak Ridge was having their hottest summer in 20 years with heat index numbers around 105 degrees F on some days.
There were plenty of former US national team rowers competing, though I'm not sure how many are former Olympians. I had a chance to chat with a fellow in my hotel who rowed at Yale in the late 40's and was a spare on the '52 US Olympic team. He had lots of interesting stories to tell (and was still competing).
All in all it was a lot of fun. I was fortunate to be rowing with a great bunch of guys and finished with 2 gold, 3 silver and a bronze, so it made baking in the sun for 4 days that much more bearable.