From a personal perspective, watching the time it takes for new tabs to load and then for the new pages to load in the tab, I’m a bit disappointed in the speed of IE8. Even Maxthon, which uses the IE8 rendering engine is much faster opening new tabs and web pages.
My experience from testing Firefox 3.0 a while back, indicates that it is still the fastest browser available. However, constant browser crashes and web site incompatibilities kept me from thinking seriously about using it long-term.
So, that said, speed isn’t everything. Still, the IE8 team needs to do a better job improving the speed and performance of IE8.