I have Opera, Chrome (bleeding edge), IE 8 and Firefox 4 beta. I rotate through them for various reasons. At the moment I use FF4 and let mozilla get all the "telemetry" data they need so make this release a good one. It would be a shame to see only Chrome and IE in a reloaded version of the browser wars. I like seeing more players just to keep things interesting.
What annoys with various browsers currently:
FF4 - any Java applet that displays a modal dialog will crash because the OOPP thingy does not detect the window so it thinks the plugin crashed and kills it when it timeouts (devs are aware of the problem and will work on it)
Chrome - simply put, it lacks NoScript - I like choosing what runs on my machine
Opera - I cannot use LastPass with it except with bookmarklets and those give just half the functionality. On the positive side, I saw it render IE9 test content almost as fast as the IE9 tech preview on my machine. Seems they have some GPU renedring thing in there. Kudos. Now integrate LastPass and I'm sold