The new version of autoblog plugin (for versions from 1.8.5 to 1.9.1-beta) has been released at this new address:
This plugin creates a new blog when someone registers on b2evolution. For every new user registration a blog and the corresponding category in the blog will be created.
The plugin has several options built in:
You can choose if you want to use stub files or not, with or without extension, if you want to store stub files in separate directories or all in a subdirectory.
You can also decide if you want to give users administration rights and own media folder on registration or not, and set the default descriptions and default skin for the new user's blogs.
Have a look here for detailed instructions and download:
The site is italian but the instructions are in english.