I am a wordpress site builder, and i consider this plugin as a "MUST HAVE" plugin.
It comes very handy when your doing ex/in-tensive testing of a wp site.
Just ONE CLICK and everything is clean again!
I am not sure about it's functionality in a WPMU setup, maybe somebody can tell some more about it.
PS: i did add it to my WPMU (test) site, and when i did a RESET
it did -POEF!- and the site was ruined :-)