I must not do popular races since I've never run into a closed field problem
I use bikereg, and knowing the guys behind it, having used them from almost the very beginning (to promote races), I'm a huge believer in their system. For me it works really well.
For races that you "want" to do, you should research them in advance. The reason the field filled in 5 minutes is because enough people that wanted to do the race actually researched their races and registered for it the minute it opened.
Having said that your app may find traction among the racing community. There's a reason why algorithmic trading is so big compared to manual trading.
cdr