Great -- just get a good waterproof case

US Rowings 2011 Rules of Rowing now allow your iPhone with this app to be used in registered regattas. Just make sure you have a good waterproof case, and you securely mount it in your shell (duct tape is a wonderful thing).
Yes, its not cheap -- until you look at the alternatives. Works in any shell your club has, accurate rates and distances even when youre not on a Class A fully-buoyed course, and it tracks everything you do.
A serious app for serious towers...

REZ2 about CrewNerd for Rowing & Paddling, v2.2.1