Hi All,
I'm going to release a plugin that I created a year ago. I updated it and added some new features and it works nice now.
-It allows bloggers to edit theme stylesheet (like wpcom custom css paid upgrade)
-You can enable it for all or specific blogs (i.e. premium blogs)
-It uses a simple method to strip insecure or invalid CSS codes.
Download it here: WPMU Custom CSS (This address may change later)
I'm going to make more free plugins for WPMU community, so please let me know your needs.