This is a helpful application that doesn’t exist yet, that I know of.
It works inside Mail. It lets you select an email message, or text inside an email message, select something from a contextual menu, and have your Address Book automatically updated with the phone and address in that email or text.
Even better, possibly, is an application that can scan all your emails and find the ones with text that looks like contact information (numbers formatted like phone numbers, and “Street” or “Drive” or variants). It maps the sender addresses to your Address Book entries, and offers to change them all en masse.
Even better than that would be an application that, in addition, does this when you first receive email, and makes the changes semi-automatically. By “semi-” I mean it presents you with exactly what information it’s going to change first, and allows you to edit what changes it makes or cancel them individually. (Something I’d really like to see more of in Sync Services, by the way.)
Time and time again, I look up someone’s contact information in Address Book, and it’s outdated. They’ve sent me an email with the new information, so I have to hunt for it, and do the tedious cut-and-paste from one application to another.
I would pay for this application.
Better make it fast, though; sounds like Audigone material.