I already made the switch to Opera because Firefox, Google Chrome, and Internet Explorer 9 seem slightly or much slower then Opera Web Browser. Plus, the constant updates for Google Chrome and Firefox seem kind of annoying since a new version comes out every few weeks or months. I notice Opera Web browser crashes less then Firefox, Chrome, IE 9 on my older computer. Opera is a fast, stable, and simple web browser for someone who just need a web browser for browsing the web, playing flash games, and watching online video.
I also like that I can move my address bar, and tabs bar to the bottom of Opera yo give the allusion of having more monitor space because the top of my web browser has no toolbars because they are at the bottom of my screen.
http://www.opera.com/browser/
With groundbreaking speed and innovative features, you can take control of the Web like never before.
Indeed, this is one of the reasons, I am now using Opera as my main browser since Firefox seem to slow down after a long time of use. Plus, pages in Opera seem to load 1 or half a second faster even on very fast sites like Google.com which is one of the fastest loading websites in the world.
Scrolling up and down websites also seem a lot smoother in Opera compared to Firefox, Chrome, IE.
Opera also has a lot of cool extensions/plug-ins : https://addons.opera.com/en/addons/extensions/
I don't think I will be moving from FF. It has been 3 years and still FF ftw for me! but yes, if it does get crapper then I might also switch to Opera browser.
Opera since it use less RAM then Google Chrome on my computer running Windows 7 with only 1GB of RAM which can be painfully slow on many modern web browsers except Opera in my experience.
If you don't like the user interface, you can change it by downloading and installing a new theme at : http://my.opera.com/community/customize/skins/
I find the user interface similar to Firefox except for the sidebar/panel on the left side which you can easily remove in the ptoolbar settings.
