Opera is not only a great browser, but it's changed the whole way I use the net.
The combination of Wand and mouse gestures means I never have to remember a password. One click gets me in to where I want to go.
Great customization gives me maximum screen space, and allows me to tile pages so I can be on a chat board, and have several live pages updating (at different rates) with latest sports scores and so on.
Tabbed browsing really means tabbed browsing in Opera.
Zoom and fit to width are mindblowing.
The Notes feature is great.
It's faster than Firefox and IE (I've tested it).
It's more secure than any other browser. Just check out Secunia if you doubt this.
Integration of mail, newsfeeds and newsgroups means I now run one screen only, and have everything to hand. And all in less download than any other stand-alone browser.
Skins... well the choice is endless. And you can pretty much put the toolbars where you want, and add pretty much anything you want to any toolbar. See: http://www.permuted.org.uk/operatool.html
Yep, fair to say that Opera is the best browser (in fact the best application) I've used in 17 years of running a PC. And it keeps getting better.