The major problem seems to be that appointments made on the iPhone aren't being synced to iCal; although iCal to iPhone seems to work fine (updates from the desktop are put onto the iphone).
Color me lucky, but so far I've had no problems syncing calendar events, in either direction. Although I can probably count on one hand the number of calendar events that I've created on the iPhone versus the hundreds that sync from my Mac to my iPhone.
What about you? Any problems syncing iCal to your iPhone?