I use Opera, and I'm surprised that of 100 votes, just 2 prefer Opera
I guess it's like Linux, the user base is really smaller than it "ought to" be.
Anyway, I've been using Opera for years, since 2002 I reckon. I've often had old and slow computers and Opera has in general been the fastest and least resource hungry browser. Browsers like Netscape/Mozilla, and also Firefox, were just too slow on my machine, and IE4-6 too insecure. Yes, I used Windows in those days. (Still do, dual boot OSX/Win7)
I've been using Operas synchronize-feature for a couple of years to have same bookmarks and setup on different computers and operating systems, and mouse gestures - I can't use browsers without them (yes, they are available for other browsers now, but on slow computers Opera still is no 1).
I don't like the looks of Chrome (and find it lacks features/settings), I've never got along fine with Safari either. Maybe I'm just stubborn.
So, Opera on OSX, Win7, Linux and phone. Most of the time I use Beta-versions, I find them stable enough. I try alpha-versions when I'm curious about new functions though.
http://my.opera.com/desktopteam/blog/ (development versions of Opera, currently v 11 betas)