Well, it took a while longer than most expected, but is has finally happened: Apple's Mac OS X Leopard v10.5 WWDC Preview Beta has hit two torrent search sites.
This piece of news is unlikely to shock anybody, if only because of the precedent, and it is expected that the Apple legal will treat this in pretty much the same way they handled the same thing happening to the Tiger preview.

In December 2004, Apple sued three men, as well as unnamed others, in federal court in San Jose, Calif. The company said the men had posted developer versions of Mac OS X 10.4 Tiger onto BitTorrent file-sharing servers ahead of the software's official release. It settled one of the cases in March and another in April.

It seems unlikely that after the Tiger event, Apple is not more prepared to handle the situation this time, since they must have seen it coming. However, they may be better prepared; but there is little they can do to stop the spread of the developer preview version once it is in the wild. Posts on various forums have already begun to appear from users who are trying it out.