Well, I'm going to be a dissenting voice and say I still have issues with Opera. It seems to encounter problems with some css formatted pages and also fails to handle javascript which IE, Mozilla (and all Gecko based browsers) and Konqueror all manage perfectly. In fact Opera shares the javascript problem with IBrowse.
Speed is good, but speed is not everything. I use Phoenix on Windows and Galeon or Konqueror on Linux. Opera is installed on both, but will not become the default browser until it handles all the pages the others do with the same results