In fact, between the big 3, there's an unceasing chase. Sometimes IE is first, sometimes it's chrome, sometimes Firefox. The fact to the matter is that they are emulating one another and all keeping moving forward.
Safari is improving too, but does it have competition on mac ? There's a sort of monopoly. So, no hurry for them, but they are following the movement too.
Yeah, the intense competition is great. Safari 5.1 was released soon, and had some canvas performance improvements, but still doesn't reach a solid 60fps on my machine. (I was testing on Windows - I think the Mac browser is faster and better - I don't think many people use Safari on Windows anyway.) Still, I think Firefox and Chrome work on Mac, so there's still plenty of competition for Safari. Opera and Firefox have mobile browsers and Chrome make the Android browser so there's good competition in mobile browsers as well.