Best practices for handling duplicate contacts among users

[MemphisJim]

I would like feedback on how some of you deal with multiple users creating duplicate contacts within an account. The problem is that I have both Windows and Mac users who would like to continue using their regular email clients for communication with customers. Some users are using Entourage and some are using Outlook.

I have programs for synching contacts between these email clients and Salesforce. However, the problem arises when multiple users have the same contact. If I were to simply merge the duplicate contacts into one, then only the person listed as the owner of the contact would be able to sync with that contact.

How do some of you deal with this situation? Do you just allow multiple copies of the same contact, each with different owners, or do you have a better way of allowing everyone to sync with one copy of a given contact?