If you want to start one, IE8 starts faster, runs faster, is just as quick in browsing, and is pretty much just as secure as Firefox.
Frankly they are both great, no reason to bash IE any more. There are some sweet features in IE8 as well.
Yeah, although I only have IE8 on my Windows 7 install, I do have IE8 and FF on my XP drive. I can definitely say that IE8 starts up faster (at least on my machine). Actual page loading seems fairly close between the two, but that initial startup with Internet Explorer is much better then FireFox.
I also prefer the text in IE8 over FF, although I'm sure if I messed with the settings, changed the display font, etc., in FF I could match it. I guess I've just been too lazy to toy with the settings though. Either way, just with the default settings I like the IE8 more.