For those not already familiar with Opera, I strongly suggest you check it out. Not only has it been my favorite browser for years, but there is really nothing comparable out there. Period. Linux or Windows, Opera is what I use. Mozilla is its closest competitor, but it still has a ways to go.
The main reason I've stuck with Opera for so long is, if for no other reason, because it remembers all the sites that you had open before something went awry or you shut the system down. Let's assume that you, like myself, always have at least 20 browser windows open. Now, let's also assume that the browser crashes, your computer craps on itself, or something else happens that causes the browser to die. With Opera, when you bring the browser back up, you are exactly where you left off (there is an option to disable this). I think the importance and usefulness of this feature is self-evident and so I won't elaborate further.
I said that was the main reason, there are many more. Opera is extremely fast. I regularly have 50+ windows open and it never misses a beat. It's infinitely configurable which is ALWAYS good (you really can't understand this until you start playing around with all of the options). You have the ability to completely turn off pop-up windows. This has been a feature of Opera for a while. Ok, I have to stop praising everything, but only because I have a lot of schoolwork and really need to get back to it.
I'm not trying to convince anyone of anything; Opera will do that on its own if you give it a chance. If you are thinking about trying it out, be sure to get Opera 7 (beta) as it was completely re-written from scratch and is much faster and obviously more standards-compliant than its predecessors.