This means your taskbar stays uncluttered even if you have 15 or 20 browsing windows open. Opera also provides a number of options that the other browsers don't. On each window, there is a drop down menu that allows you to zoom in or out, which is especially god for people with bad eyes. Opera also allows you to turn images on and off with the click of a button, set a window to reload every x amount of time, and save all the windows you had open when you shut Opera down, so that they all open up when you start Opera again. As for actual web page performance, opera is a speed demon.
Opera does have a few problems, of course, but nothing too crippling.
Also, most internet software that integrates with a browser doesn't recognize Opera, but that's also minor. This is really only a minor inconvenience, and the ads can be ignored fairly easily. All in all, with version 5, Opera Software has brought their browser into the big leagues. It may not solve the problems of the world, but it will give you a much more pleasant browsing experience. That's what they said about rock'n'roll.