If you have your contacts set to sync with Google, you can just go to settings - applications - contacts and clear data. Exit back to the home screen and open contacts, then skip the BUA log in.
Anther way is to go to the contacts list and go to one of the dulpicates. select the "g" under Connection (with the chain links symbol), then at the bottom click on the "Join another contact", and select the contact to be merged with. I had several where it looked at the phone number and the email of the same person as seperate contacts, not sure why. Hope this helps as well.
Had this issue too, I disabled sync with my google contacts and manually fixed them all, anyone know if turning sync bac on will mess it up again, Im afraid to turn it on...