I've used Firefox for years, and it's never been as flaky on OS X as it's been for the past month or so.
Of course I don't know whether the problem is Firefox, Google's web apps, or OS X 10.4. All I know is it's getting miserable.
Firefox loses track of the cursor position in wysiwyg edit boxes. Firefox pegs the CPU. Firefox sucks memory. Firefox crashes.
If Safari worked with Google I'd switch. I may try Camino again, though it uses the Firefox rendering engine.
I don't see many other complaints, so if you're having trouble leave a comment or two. Maybe it's just me.
Update 2/28/2008: I had to go back to Firefox -- at least for Google properties. Safari has too many problems with Blogger, and it doesn't work at all with the page editor. Some of the problems, such as pasted text showing up outside Safari's rich text editor, have to be at least partly Safari bugs.
Update 3/4/2008: Now I'm trying Camino, which has gone through a few point updates since my last try. It certainly feels bloody fast, and so far Google is treating it like a first class client. It would be nice if it has fewer memory leaks and SPBDs than Firefox.