Well, when I was exchanging tweets with @dsubies I said that I am an Opera user and he asked me why I use Opera. Since 140 characters are too few to explain it I said him that I will answer him here. Well, long after that, here is the answer.
At the time I started using the Internet the only serious alternatives were Internet Explorer (I'm sorry, I said serious) and Netscape Navigator. Then I discovered Opera, which included interesting innovations like tabs, pop-ups blocker and a download manager. Approximately at the same time, I started using Linux and one of the more exasperating things were the horrible look, the uncomfortable toolkit, which I think it was some Athena variant (I can't explain this, those who lived with this will understand it) and the instability of Netscape for Linux. A few later, while Netscape slowly died in hands of AOL, Firefox appeared, characterized by its resources voracity and its slowness, increasing my bet for Opera. If you add this to the fact that I used to have old computers, I really needed to use a light and agile browser.
