I've used the site a decent amount in the past month and agree with others that it is a great idea. Here are my major suggestions (some echo what others say).
1. Putting in off-peak amount for airlines that offer those specials (i.e. AA)
2. Including fuel surcharges, as they can make an award ticket "not worth it". If it is too hard to put a certain amount in, you could use a yes or no.
Other than those two things, I'd simply say that you could add more airlines. Overall though, this is a great tool.