in terms of speed it plays out like this
1) Firefox 3, Chrome Beta (basic surf Chrome wins, advanced surfing Firefox wins)
2) Opera, Safari 4.0 (some claim it is as fast as Firefox 3, still waring over it)
3) IE 7
If you are still using IE you need to hit yourself and download one of the alternatives above!
I'm loving Chrome, think I have every angle tweaked on it, its pretty dang fast, but struggles with Flash and some video plug-ins. But thats the beauty of open source, especially with a project like Chrome, since the best and brightest programmers around the world want to see IE fail and open source thrive there is no doubt that it will grow, question is, can it beat out Firefox down the road.
In terms of market share the only reason IE has a leg up on Firefox is because most internet users are not savvy enough to install the alternatives, they just stick with the default Windows crap, same reason MSN search has 10% of the market, most people don't know how to change their default search