The iregatta app works well, I've had it for a couple years and played with it a few times.
The phone however doesn't work too well around it. The battery life on the phone is very short while running the app. The screen is nearly impossible to see in the full sun and the touch screen is about useless with wet fingers.
That's been my experience with the apps for this kind of stuff too. I have a velocitek prostart that I use on my J boat that shows speed, shifts, and allows you to set the start line (giving you distance). I think you can really go nutz with that data but I have found that having a speed readout has really helped me transition to the monohull faster. We haven't been using the start line info lately because it's pretty distracting.