Susan mentioned Opera 11 in her recent column. I have been an Opera user for many years, but v11 was too buggy, and I had to reinstall v10.63. Many other users have had difficulty and some have done as I have. There is a particular difficulty when using Opera 11 with Yahoo Mail Classic, as the latter becomes almost unusable in certain respects. Also, some websites become difficult to use where there is a basic page with specific information added, e.g. for your own account.
That said, Opera is very fast, and almost infinitely adjustable. Although I also use Firefox, Opera is the better browser, v11 apart. YMMV of course!