When troubleshooting iPad/iPhone sync issues with your MacBook (or whatever)
running OS X 10.6.8, this will help you:
defaults write iCalExternalSync debugLevel full
tail -f ~/Library/Logs/iCalExternalSync.log
It still took quite some time to spot the duplicate (exception-) dates in
recurring events, but deleting them manually, re-synching and adding afterwards
did the trick. Not sure where this duplicate dates came from, but I suspect
that it has something to do with timezone support being off by default in
iCal.