I currently have contact information at several places:

• old PDA's address book
• mobile phone's phone book (primarily name, phone number)
• email client's address book (primarily name, email)
• web mailer's address book (primarily name, email)
• instant messenger's contact list (primarily name, im, email, birthday)

And there are several social or business networking sites on the Internet where contacts provide information about themselves, like LinkedIn or XING.

All those sources can export as vCard, but as you might imagine, I get a lot of vCards for the very same contact that way. Are there any tools where I can import them and then merge them (it may ask me which phone number is more current in case of field clashes of course)?

Bonus points if it can track which information I have discarded so when I re-export all information from one of the sources I can't import to (networking sites), it won't ask me again if I want to overwrite phone number of person X with the same ancient number...

I hope you understand what I try to accomplish, if not just ask :-)