I have set up a Professional Web Design microblog which is indexed by Google and works just like Twitter - in fact you can link your Twitter account to auto post so you don't need to post twice, but here's the really neat bit, we allow you to do-follow backlink to your project websites from your profile and tweets. It's specifically for web designers to show off work and get a fast backlink, spam posts are deleted to maintain it as a good neighbourhood. http://webdesigner.status.net/ enjoy!
That's because it's only just been created and there are only half a dozen users just post messages as if there are tons of people, it doesn't matter that there aren't, if people 'get it' it will fill up soon enough. If you post a link in your tweet/message it will appear in Google, as will the link from your profile to your site. I use it to post a link to each client site I create. It's a fast easy way to build back links. You may want to set your username to one of the keywords you want to rank for, that way 'WebDesignNYC' or whatever userrname you choose links back to your site and looks like a contextual backlink to Google. Search Google for inurl:webdesigner.status.net and show all similar results and you will see every post is indexed by Google, complete with backlink. This is set up exactly the same way Twitter was before Google asked Ev to add rel=nofollow to all Twitter post URLs and why Twitter was so great for SEO.