I just joined identi.ca. identi.ca is a microblogging service based on an open source project, Laconica, and all of the updates are copyrighted by a Creative Commons (Attribution) license. You can log in using OpenID. All really great stuff. I imagine, too, because it's based on an open source platform, developers will begin to code in data portability (or have they already?) The documentation is a bit lacking, and it's clear that it's a very new project. There are an increasing number of third party apps that can use it (it supports the Twitter API.) So I'm on identi.ca now (follow pearlbear). Like all social networks, they are only as usable as people in your social graph use it, and it's pretty sparse for me right now. But hopefully that will change.