Mark Pilgrim talks about CSS hiding tricks that relies on bugs. David Hyatt at Apple would like to fix them - they are bugs! Mark says that as a web developer you have to rely on them to make your site work on all browsers, and goes on to suggest that Apple should intentionally implement a few "edge cases" to hide CSS from Safari and from any other browsers than Safari.
Maybe I am missing something, but isn't the obvious solution to make a valid syntax that will say "Only read this if you are browser X"?
Mark also keeps a list of layout bugs in Safari.