Edie and I have not regularly gone to dog parks. But we went yesterday to meet another YTer--Zeus08 (aka Melissa). We had a GREAT time. See my photos under the photos section (thread name: Tucson meetup).  Anyway, there are 2 areas--for large and small dogs. The small dog area is for dogs 30 lbs and under. There is a sign at the double-gated entrance explaining this.
 
We had a great time, and then at the very end, a guy comes in with a GIGANTIC dog (I am guessing 60-70 lbs). I couldn't believe it. The big dog area was only yards away. I think he wanted to come in because his buddy had a small dog. The big dog was OK, but we did not stay long after that. 
We met lots of nice little dogs. I was very impressed by the facility. The grass was perfectly groomed--almost like a golf course! And everyone was picking up the poop, so it was very clean. 
We will go again.