Do you have duplicate names in your address book, but only partial information inside each one. Perhaps you have the mobile phone in one, home in the other, etc. You can easily merge them into one card.
Here is how to do it:
1. Open Address Book
2.Switch to Card & Columns View by pressing COMMAND-1
3. Hold down the Shift key and select the cards you want to merge.
4. Card -> Merge Selected Cards.
5. Now you have one card. If you have any redundant information, simply click the 'Edit' button and remove it or add to it.