@gollum,
Eventually a2k's new platform is going to support personal blogs, but some other ones major platforms that already exist are Wordpress, tumblr, and blogspot.
In terms of audience tumblr is, in my opinion, currently the platform best set up to draw an following on the platform itself, most other blog platforms just let you have a blog and expect you to get the audience (this is actually one of the things the blog platform we are building will try to help solve).