ive been on quite the journey with my mac browsers. When i first got my mac 4 years ago i was so used to firefox that i stuck with it. This was ff2 btw. This is when i discovered camino, which was Gecko, the rendering engine ff uses, but written in cocoa, it ran so much faster, and had integration with OSX in the form of using the native dictionary and things like the keychain. it also loaded almost instantly, compared to ff which took 20-30 seconds to load, when turning it on initially. Then ff3 came out, this was when they made major progress into streamlining the mac version, it ran much faster, and the improvement in Gecko, which would take a while to come over to camino, was worth it in my opinion to not have a native app.
i used ff3 for a while, but then, safari 4 came out. I tried it for the first time, and was blown away by the speed of the browser, its soooo much faster than ff ever has been, even now. rendering pages took drastically less time, it severely impacted my browsing in a good way. it also ran much better than ff. A bit later camino 2 came out with the improved gecko engine, but it still coudlnt compete with safari for speed. i used safari for quite a long
Then when they finally released chrome for mac, i had tons of trackpad problems with my mbp, so i never used it, though it seemed fast, i stuck with safari.
but then just yesterday, i went and got the latest dev release for chrome for mac, and noticed right away that they werent kidding a couple weeks ago when they talked about the major improvement to the Java Script rendering, and the trackpad issues were gone. The JS implementation in safari is really very good as well, but cant compete with chrome, and actually it was Head Fi that put it over the edge for me, now that its so JS dependent, chrome makes the sight that much better :D
So now i am happily on chrome, though whenever updates come out for safari i will go check it again.
I also realize that some people are addicted to using extensions in ff, and so they will never leave it, like one of my friends would never use safari because he would have to quit using grease monkey, but i was never a fan of extensions, so it didnt bother me.
The only problem i ever had with safari, was that if you put a tab group as a bookmark in your bookmark bar, you couldnt command click it to open it in a new set of tabs, whcih worked in ff and camino, and it also works in chrome. i was forced to open a new window just to view those 4 tabbed bookmarks i had.
Another point, is that safari and chrome pass acid 3 100/100, i dont believe ff does, nor is it gonna be html5 compliant as soon.