I've gone a number of times years ago. It's a great time.
I found the most fun was just walking around the booths and seeing the variety of dogs. All of them are friendly so it's like one huge petting zoo.
Some of the show part seemed a little stupid with people prancing around with their dog - but it was entertaining in itself.
One great thing (if they have it) is Jack Russell racing. They have it set up so that maybe 20 Jack Russel dogs come out of chutes and chase something while jumping over little obstacles. It was really fun to watch. Those little dogs are fast as shit.
So go. You'll have a great time and the entrance fee is usually pretty cheap.