Opera is actually a pretty good browser (geekery)
At least on Windows, it's pretty nice. It feels a little faster than FF3 (although TEXTAREA is a bit laggy), and its default key bindings are irritating but it was easy enough to fix those and make it behave exactly like Firefox. I really like how UI-wise it actually works with the native GUI instead of tring to do its own thing (unlike, say, Firefox or Chrome), and it's also the only browser I've ever seen which does a good job of doing smooth scrolling which still feels responsive.
So far the only bug I've run into is that the background on my 404 error animation doesn't move, which tells me there's something weird with how it deals with CSS background-position in DHTML or something. Also, there doesn't seem to be any way of adding a resize widget to the lower-right corner of the window (the default skin had one but this other skin doesn't). I'm sure there'll be other problems as well, but I think I'll give this a try for the next few days and see how it works out for me.