WOW i was looking for some thing like this a long time.
1) It works with Shar DB in a MultiSite Setup
2) It dumps all the tags that are not used.
Now some stuff i would love to see
1) Mass Delete Old Posts Well we have about 124,580 Posts Lets say if post is older then 1 year dump them also in batches of 50 well i can tweak it to do 500 at a time server has lots of power to handle this.
2) 14,238 Categories same story here
The plugin can be a one stop clean up shop .
Thank you Kindly