jaiku
I’ve been playing with Jaiku a lot lately.
My username there is Emory. So far, I like it a lot better than Twitter, though I wish they used OpenID (like every other web application should) and I hate maintaining Yet Another Buddy List.
The deal-sealer for me? They have a sweet mobile client for S60 V3 devices, so I can easily do status/presence updates as well as location from my N95. And it also tells you when a contact has an appointment or will be busy. It’s rather awesome.
Update: the latest version of the mobile client sucks the battery down on my N95 like you wouldn’t believe. I can’t go a workday without the battery getting low, and I went through all the usual steps to make sure it wasn’t something else, I promise it is the Jaiku mobile client.