Hi Moujiik, there is a script that will delete styles without any objects on them here:
http://moi3d.com/forum/index.php?webtag=MOI&msg=3774.2

To use it you'll need to set up a new shortcut key and paste in the entire script into the "command" part of the shortcut key. Then when you press that key any styles not assigned to any object should get removed.

- Michael