I so identify with anyone who has this problem of having address book duplicates. Took me at least five tries to get it right!!!!
The directions that Apple gives only really work if you only have one device. There are very few articles that deal with the problem of coordinating multiple devices so it was a trial and error effort to make things work.
I have 6 desktop and mobile devices attached to my account and wanted them all to sync using ICLOUD. I'd get one or two set up and then the next one would add in the duplicates. Was making me crazy. Here is what I finally did to solve the problem:
1. Using your desktop app, export a clean copy of your address book to your desktop. If your file is contaminated with duplicates already, go back and find an older copy.
2. Using your desktop app, delete all of the entries. Then go to System preferences and turn on the Cloud for Address Book. It should be empty.
3. Turn the cloud off for each and every device you own. It will ask if you want to save the contacts or delete them. Choose delete.
4. Every device will now be empty of data.
5. I was unsuccessful at bringing my data back in using the Cloud web site. So I went back to my desktop app and brought it in that way. Then, I turned the Cloud back on. If you've done it right, all you should see is the Cloud symbol above where it says ALL CONTACTS. Immediately, all of my devices filled up with the same information. I double checked by adding a new data entry. And all of the devices updated with it.
The next day, I noticed that my desktop app was not doing the cloud updates, although all of my other devices were. So I went to the desktop app preferences, deleted the entries and then turned the cloud back on. Immediately the desktop app updated with cloud contacts. Now, it syncs just fine.
BTW, everything is done by an "air sync" and if you actually connect your device to ITUNES, the address book will be greyed out. Don't change the setting. You don't ever want to sync the data with ITUNES again -- or you'll get your duplicates back!
The iCloud is genius. Sure makes life simpler and easier. So if you have problems in the beginning, don't give up. The end result is so worth it!!!