This is a huge step forward for the creation of an alternative to Twitter, in numerous ways, some obvious, many more subtle.
Reading through the project's goals and philosophy, this truly looks like a promising contender to provide what earlier attempts to replace Twitter have been lacking. Tantek highlights:
Micro.blog is being built from the start to interoperate with heterogenous systems (i.e. not just with other micro.blog instances, a big distinction from many previous open source decentralized web efforts which focused primarily or exclusively on interoperating only with themselves).