If you followed the steps in my post from August on merging your Outlook and Gmail contacts, you may have ended up with duplicates in your contact lists. Microsoft's advice for deleting duplicate contacts is to sort them by the date modified, Ctrl-select the ones you want to remove, and press delete.
The problem is, the duplicate entries probably aren't identical, so you're almost certain to delete some data along with the dupe. What you need is a way to merge the information in the duplicate contacts. There's no such feature in Outlook, but if you're willing to spend $30, you can make short work of your extraneous Outlook entries by running 4Team's Duplicate Killer for Outlook.
The program deletes or merges duplicate e-mail messages, calendar entries, tasks, and notes in addition to contacts. I tested the program with Outlook 2007 but, according to the vendor, it works with Outlook 2000, XP, and 2003 as well. The new version, 3, is said to work with "Microsoft Exchange type folders including public folders," according to the vendor's Web site, but I ran it on a standalone Outlook installation.