I finally remake the themeperpost plugin to theme per Author to create a group blog using custom post type.
Admin can set theme per author from the dashboard. The option is visible only to Admin.
Does anyone want this? Please let me know
Now I am working on Binding category to authors. If this is finish,
A multi blogs like WPMU is possible using custom post type.
Help is wanted for Binding category to authors. Role scooper is too big. I am looking for a few lines of code/function that will do the job.