Here's another weird one. An SMB share I have on an OpenFiler machine that worked under 10.5 failed to mount correctly under 10.6. It would mount, but the permissions on the share's root directory would be set to 000, and the Finder wouldn't allow me access, saying "The folder xxx can't be opened because you don't have permission to see its contents." I could still see the contents from the command line.

Turns out that it's because the "primary group" of the share was a group that my user was not a member of, even though a group my user was a member of was set to have RW access. It started working properly once I set the "primary group" of the share to the one I was a member of.

The share worked properly under 10.5 and works correctly from every other SMB client I've tried. I don't know what Snow Leopard is doing to create this problem.