I was messing around in my Yahoo Mail address book trying to export everything so I can clean up the details using Excel instead of loading the Yahoo interface back and forth. I noticed that they’ve added a duplicate clean-up tool to their options under address book. You’ve got to go to the details of Mail Options and then to Contact options to get there.
The interface works pretty well. You have the option to automatically merge exact matches with a button click. Then you go through a stepped process of reviewing similar matches next to each other with a preview of what the merged contact information will look like.
Very user friendly.
Just go to Yahoo Mail, then to your Mail Options link, then choose the “Contacts Options” category. The “Clean Up Duplicates (beta)” link will be on the far right, middle of the screen.