I like Opera myself, I think it's a great browser, probably a better one than Firefox in terms of functionality. I used to use Opera instead of IE before Firefox existed, especially as it was available in Welsh. I switched to Firefox (well to be precise I switched to Mozilla first then later to Firefox) because I just like the feel of it better, and also because Mozilla and Firefox are open source, something I strongly believe in. I hope Opera continues to thrive though, as well as Firefox. As long as everyone sticks to the standards it's all good :)

At work we test our public web site and web applications on IE6 and the latest versions of Firefox and Opera (and make sure pages validate using the W3C's validator). Generally we develop mainly using Firefox then test on the others. It's unusual for us to have to do anything to get stuff working on Opera, but getting stuff to work properly under IE6 can be a pain though and we can spend ages fiddling with the CSS.