Cardfile.org just launched. It’s free. You create an account and enter your contact information and they provide an RSS feed that your friends can subscribe to so they’ll know when you change phone number, email address, postal address, IM account name, all that kinda stuff. They give you the HTML you need to stick on your site so your friends can get to your information easily. In addition your friends can download your contact information in VCF format. And if you can get your friends to sign up you can add them to your list of tracked contacts.
No, the idea isn’t perfect. I wouldn’t put the supplied HTML on any web page anywhere, for instance … at least not for my personal contact information. And there have been a lot of companies that’ve tried this in the past and died away. Hopefully they’ll listen to feedback and this one will stick cause the basic idea is a really good one.