Go get SKTools and you can delete duplicate calender, duplicate eventw and duplicate contacts at the push of a button.
http://www.s-k-tools.com/index.html?sktools/m_feat.html
There is a trial version but will only let you delete 5 at a time. Totally worth the money, I think its like 10 bucks. It also optimizes and compresses your registry and if your phone is not yet flashed, you can make registry changes from the program itself.