I've implemented bucket-destroy, a multi threaded utility that does everything it takes to delete a bucket. I handle non empty buckets, as well as version enabled bucket keys.
You can read the blog post here http://bytecoded.blogspot.com/2011/01/recursive-delete-utility-for-version.html and the instructions here http://code.google.com/p/bucket-destroy/
I've successfully deleted with it a bucket that contains double '//' in the key name, versioned key and DeleteMarker keys. Currently I'm running it on a bucket that contains ~40,000,000 so far I've been able to delete 1,200,000 in several hours on m1.large. Note that the utility is multi threaded but does not (yet) implemented shuffling (which will horizontal scaling, launching the utility on several machines).