Rick.. the preregistering system you have is great, it's a great way to see who might be coming.
However, I think it would be a good move to have people preregister and pay at that time.
It would be easier for your planning purposes, plus you would have money ahead of time to finance the event.
If you had a late fee cut off date it would make it simple for you to order the right number and sizes of shirts and etc.
In addition, you wouldn't get as many people registering and not showing up.
We're considering using The Regatta Network for all our regattas in the NE this upcoming summer. It takes a couple dollars per entry but well worth it to make it easier for everyone.