I'm very impressed with the new IE 8.0 - so much so I've now dumped the Firefox 3.0.11 and made IE my default browser once more.
I surf with the default text size blown up to make it easier on my eyes. A recent Firefox update (not sure which one) introduced a bug which caused the text size of the page you're reading to suddenly reset to the default, which is annoying.
I've also noticed that the later versions of Firefox have slowed down considerably. While I'm reading a page, I'll open several links in tabs as I go so that I can have the pages ready in the background when I'm finished with the current one. Lately, it seems like something is hanging so that I frequently find that none of the pages in the other tabs have loaded at all. It happens on enough different sites to make me think the problem is in Firefox. Sometimes I've had to "PSKILL FIREFOX".
Now they've finally gotten round to adding a decent "find" function to IE, it seems to me there's no reason to go back.