I was looking for an AppleScript that would just show me the duplicate entries in my Address Book, and not delete them out of hand, since some have different information yet the same name. I could not find one, but found this great gem from Apple Developer Documentation - Apple Script:
osascript -e 'tell app "Address Book" to get the name of every person' \
| perl -pe 's/, /\n/g' | sort | uniq -d
It will give you a nice listing of every duplicate entry in the Address Book, making it easier to sort through them for information and delete them individually.
Mac OS X Hints
http://hints.macworld.com/article.php?story=20060322202753429