There's a couple things that could have happened. The one we see the most: users start seeing contact dupes after they reset their phone, add Dashwire, and then connect via ActiveSync to sync thier contacts. This is a known issue (
http://dashwire.com/help/issues), and happens because of the way that ActiveSync assigns unique IDs to contact entries. For future reference, if you're an ActiveSync user, then you'll want to add contacts via ActiveSync before you add Dashwire to your new or recently reset phone. That way, you shouldn't see any duplicates.
If your scenario is different from what I outlined above, let us know about that as well.
New sync architecture in the works that should prevent this from happening in the future. Thanks for the patience