Not so much in how fast words and images are displayed, but how fast Javascript is executed, how quickly Flash and Java are handled, that sort of thing. For AJAXy web pages like
ESPN where there are all sorts of dynamically-generated menus dropping down and ads playing while at the same time Flash video is playing, and there are wildly different mouseovers for every link on the page.
But mostly how it loads in 2 seconds instead of 10 seconds when you start it. Firefox 4 has caught up in that regard, it now loads in 3.5 seconds.