It would appear that Apple's forthcoming OS, Snow Leopard, has leaked to the web early. The developer build 10A432, which is rumoured to be the gold master build, is available on a number of Bittorrent sites, with the Pirate Bay reporting over 2,000 downloaders at the time of writing.
MacMagazine.br, a Brazilian Apple site, has a video from one of its readers of the new build. It's embedded above, though be aware that the user in question has customized icons installed. It might not look like that on your Mac.
As previously reported, Snow Leopard could arrive as soon as the end of the month, and carries a $29 price in the US. It's not clear yet how much it'll be over here.