Solution to duplicate sync data
For those of you having problems with duplicate calendar events and contacts on iOS devices, I had the same problem and found the answer. Basically there are two different places where sync settings are stored, but they are somewhat different. There are the settings on your iOS device (Settings > Accounts > Mobile Me) where you can turn on over-the-air syncing of various things through Mobile Me. But there are also settings in iTunes on the computer you sync from. If these are on, it will essentially double-sync your info when you sync your iOS device through iTunes, and duplicate the data. So if you have the OTA Mobile Me syncing enabled for those components (mail, bookmarks, contacts, etc) on the iOS device, you want to TURN OFF the syncing of those things in iTunes; there is no need to sync those through iTunes. It makes some sense once you figure it out, but it's seriously confusing at first, I think they could do better at detecting and helping resolve this situation, which many people have had.