I use Camino for my browser so the threat to my personal machine is low…but I fired up Safari and went to this test page and saw that Safari is indeed problematic:
http://secunia.com/advisories/18963
The “fix†is to open Safari preferences and uncheck the “Open safe files after download†checkbox. I would suggest using Camino or Firefox as another reasonable workaround. You might also want to make a bookmark of the Secunia site since it monitors many (8,000?) products for security vulnerabilities.
Update: This is “fixed” with the latest security update available from Apple.