Went today, the trucks were parked to the left of the grandstands facing the track. There were about a dozen vendors there. It was a race day, so there were a mix of people, from the hard core bet-on-the-ponies crowd to the more foodie focused. We saw 4-5 races go off while we were there (of the 10 scheduled)
The trucks seemed to get mobbed pretty early - the line for the Grilled Cheese Nation truck was very very long all afternoon. In the mid-afternoon, almost every truck had a significant line, and these things aren't built to put a lot of plates out in a short amount of time. My wife ordered a lobster slider and some bisque from Lobstah Love. She waited 20 min to place the order, then 25 to actually get it - and this was a cup of soup and a bun with some lobster salad on it..
I'd go again, but go early and hit the popular trucks first thing..