He was convicted of "circumvention of a technological measure used to protect a work", which is the heart of the DMCA. There's also a reference to a second case in Nebraska which involved mod-chipping a Playstation. That answers your original question, "has anyone been prosecuted successfully under this law?"
There aren't any convictions under the "disclosure" interpretation; but remember that Sklyarov was charged with trafficking in circumvention technology, even though he personally distributed no software, only information, and that is what has everyone so concerned about the possibilities.