The site, before it was taken down, encouraged users to locate Geocaching.com and OpenCaching hides, sign the logbooks, then steal the containers and their contents. MDN members were then encouraged to either (1) hide their own muggled.net cache at the site in place of the original; (2) destroy the original cache and post photos of the cache's destruction; or (3) return the stolen cache after extorting $10 from the original cache owner. Pretty sleazy to say the least, and not surprising that the site has been taken off-line.
You'll also notice references to a seemingly-associated site in the post in the link above, called, Off The Grid Geocaching. This appears to be a home-made geocaching site that requires various levels of paid memberships to unlock certain features, where members can post hides and log finds. Currently, these OTGC caches are only available in Alabama, Florida and Georgia. The "Alamogul" of OTGC is someone named, barryd52, who has a total of six finds so far.
Suddenly, opencaching.com doesn't seem quite so rebellious any more.