I have a Mac... OSX86 :-P and it kicks ass. So after playing around with all the default stuff for a few days I download firefox. Not the crusty, memory hogging 2.0 but the brand new slick looking 2.0 beta, from here. And I must say it looks really really nice on OS X. I think the developers have been really working there ass off to get it up to speed on the Mac. It's got polish and it shows. I think a lot more Mac users are visually aware of their surroundings and you really have to bring your interface up to atleast the Apple HIG if you're going to get any traction at all. Else you face losing those users to Safari. Trust me, you don't have to try hard to get users off Safari, but first impressions are important. And if the end-user doesn't like what they see in the first 5 seconds you are dead meat.
So imagine my surprise when I download the firefox beta on vista. :-\ See what I did there? Yes it sucked that hard. I know windows users aren't the same as mac users and are willing to put up with a lot more slackness. But the windows firefox beta, looks like a beta. Garish ugly blue buttons and all it warts.
Basically, it didn't blend.