The built-in web browser in Windows Mobile is pretty bad. It doesn't support tabs, and it the rendering of html is not that good. A while ago I tried Opera Mobile, and I really liked it. Right about the time that I was going to register it, Skyfire was announced, and this browser looks very interesting.
But, I haven't been accepted to the public beta yet. Since I have still been frustrated with the built in browser, I registered Opera Mobile.
Now, maybe I will look into Opera for Linux.