I had posted that some times ago on Twitter. There is a new version of the excellent GPGMail plug-in for Mail (OS X). Grab it, if you haven’t already.
Just put it inside ~/Library/Mail/Bundles and restart Mail. (More information on GPGMail’s web page.)
Edit: This is not an official version of GPGMail. There is still no official version of GPGMail compatible with Snow Leopard.