Jaiku is twitter done right. I don't know what their connection with Nokia is, but it scares me. They never had a scaling issue, so there's someone behind the scenes who was willing to pay for good architecture instead of just rapid development.
They will rule the world. Lets just hope they bring socialized medicine with them.
Mobile strategy: They have an app built for the Nokia S60 that doesn't just access the site, it integrates folks' posts into the contact list on the phone! They're in private beta of a J2ME app, which is good news because the "community provided" J2ME apps suck.