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"?
Except that Javascript can be disabled, is there a reason to not just do that in Javascript?
Mark also keeps a list of layout bugs in Safari.
I've been seeing nonsenese like this for years, ever since the second web browser of any consequence was released.
Clever Browser Bug Exploitation is just the wrong way to deal with stuff like this. That's what the browser ID string is for--identify the browser and send the right page for it. A dozen nasty hacks inside a single HTML document will inevitably bite you. A simple template and preprocessing, or on-the-fly preprocessing with SSI, will work fine, and in those places it won't the Clever Tricks likely aren't going to either.