This calendar sync issue is particularly annoying since it has been around since 3.0 (for me, at least). I never experienced any of these issues with 2.x. Like the previous poster, I now need to do a daily check to make sure my iphone calendar is correct. I've had appointments that never showed up and others that were there, but disappeared.
This is the 3rd most important function of the iphone for me (phone and email are 1 & 2, ipod is #4 🙂), so it is pretty frustrating!