I've heard people complain about inaccurate GPS data and poor battery life with the iphone, but I use cyclemeter on my iphone 4 and I've never had any issues. The map tracks me fairly precisely and I never have any weird blips or missing data, and the average speed/time matches my wired cateye computer to within .1mph/1 minute ususally. I also have to assume that people that complain about battery life are using it mounted on the bars with the screen on, because mine is locked and in my pocket and lasts a long time. I did a 65 mile ride recently in a little over 3 hours, and starting at 95% battery, it ended the ride around 55%. I don't do many rides longer than 3-4 hours, so I don't think it'll ever be an issue for me.