Depends on if you have a high number of contacts (probably in the hundreds) and you've got a high number of dupes. If one of the two isn't high, you're better off deleting them by hand.
The only alternative **I've seen/used** is when syncing with my PDA. At time dupes appear and it asks me what to do with them. At that point, I can erase dupes on the workstation and in the PDA.
-SUO