Been using this cool address book service I read about on Cult of Mac a while back. It’s called WriteThat.name. It links to your gmail/google apps account and then scours incoming email for new or updated contact information. You can then have it update your contacts automatically or manually. I also used their Flashback service to look through all of my old gmail and pull any contact information out of that.
It’s really simple to setup and it saves me time searching my email for numbers I never put into a contact record and if people update information, my contacts are automatically updated as well.
Very nice service. You should check it out here.