I think there are a couple of things to think about when it comes to wet tracks.

Firstly, I have to say I don't mind wet tracks, as long as I know for certain that's what we've got. If I know it's a genuine wet track, and it isn't going to change dramatically, then I'll bet. Nothing worse than working out all the form for a heavy track and it improves sharply during the day to be dead or something. Or working out all the form for a dead track and it rains throughout the day and gets to heavy.

As Stix pointed out, a lot of horses get scratched because of the wet, or their form shows you that they just can't handle it. However, one thing that makes it tough is that not all horses have had experience in the wet. Basically every horse has had experience on good tracks, but there are quite a number of runners at every meeting which haven't even seen a wet track. So, you have no idea if they can handle it or not. Their breeding can be a clue, but no guarantee.