What is the best way to coordinate data over the Internet?

I've recently been subject to spam-like levels of Plaxo requests. Although Plaxo does some things I like (provides a remote copy of my contacts and a way to sync work and home contact lists) I would like to think there were alternative ways to handle the coordination aspect of what they do, i.e. keeping your contacts updated automatically.

If a number of users wish to coordinate data over the Internet, what tools are available to them? There are various ways in which a casual user can serve data; they could set up a web-site/web-service or join some P2P network. However if the problem is simplified to merely becoming a source of data then they can send it out as messages, the most obvious form being email.

I've seen estimates suggesting there are about 25 million web-sites out there, about 2 million users of some file-sharing network and goodness knows how many virus infected PCs that could act as servers to somebody. But Plaxo relies on messaging; you install an Outlook plugin which can update things automatically based on the content of Plaxo generated emails.

Is that really the best way to do things? Windows and Outlook is not for everybody, and requiring a plugin reduces the numbers even more, but that combination must rank pretty high in terms of numbers.

Somehow I find all that a bit depressing...