I've used a mix of Safari and Firefox for browsing on my Mac for a while now - primarily Safari. My office PC has Firefox and Internet Explorer, with IE used mainly for internal sites that "require" IE (many of which don't have any technical requirement to use IE). Now that Safari 3 has come out, I've upgraded on both my home Mac and my work PC.
And gotten two different stories.
I had previously installed the Safari beta for Windows on my PC. I really preferred the font rendering on Safari compared to other Windows apps - the darker, fuller letters were much better to read, and I was genuinely surprised to see so many PC users blasting the rendering as being "broken". Unfortunately, the browser was just too unstable to use regularly; I was getting a crash at least once an hour, compared to almost never from Firefox and IE. It was just a beta, so I wasn't worried or surprised, but it meant that an uninstall was coming.
Now a new beta release has been made. I'm not sure what functionality increases were made, but the stability was vastly improved, to where I could now use it as my primary browser over Firefox.
The opposite has been true on my Mac. Safari just never crashed before - I never had a problem, while Firefox would occasionally (but still very rarely) crash. Safari 3 does crash on me, however. I was really surprised the first time, since Safari had always been so stable. But it now happens - well, not regularly, but often enough to notice.
It's too bad, because it's a nice browser, but I'm afraid I may have to switch back to Firefox as my primary browser on my Mac. At least until a Safari update is released.