According to this performance test available on video at The Windows Blog:
Of the top 25 most popular sites in the world, IE8 wins 48% of the time, Chrome wins 38% of the time, and FF only wins 16% of the time. Of course, they didn’t cherry pick the sites they tested. They chose the top 25 sites as reported by ComScore in December 2008.
It is interesting that Google’s Chrome follows closely on the heels of IE8 in this test. I found Chrome very quick, but like Safari, security concerns hold me back from using them regularly. I like Firefox, and with the right tweaks, it can be very fast too. I vacillate between IE8 and Firefox, not really preferring one over the other. Right now IE8 is my default browser, but that can change depending on my mood. <g>