Love the idea, and it solves a real problem. I thought of building something similar awhile back, when I got frustrated collecting fees for a fantasy football league.
I'm not sure whether this'll really work...Often when you need such a system it is when each of the participants is a little short on the money. These people may not want to use a system that is going to cost them money on each transaction.
People who don't really care about the money are probably also not going to care much about how it evens out between the group, as long as it's sort of equal.