I'm sorry... I keep trying Opera, wanting to like it, but I can't... It is just way to clunky. I don't really know how to describe it other than that... I find it FAR slower than the lightweight set of add-ons that I actually USE in Firefox. Sure, if you try to replicate every single feature of Opera in Firefox with Add-Ons, then you can certainly succeed in slowing it down to a crawl. But I don't need all of that stuff. Opera just has way too much crud that I do not need, and won't ever need (like a Mail client, what is this, Netscape Communicator?)... Built-in Bittorrent? No thanks, that's why I have uTorrent. That, and Opera 9.x had lots of problems with long-term use and the Flash plugin (this may have been fixed in 10, but I haven't seen many reports one way or the other).
And, on top of it, while they build things into the browser that you might not need, there no extension support at all. So, if I'm not just completely tickled-pink with what Opera deigns to give me, I can't get any third-party plugins to do the rest. If I can't put Adblock Plus and Xmarks (or something similar with automatic updates) on my browser, I'm absolutely, positively not interested.
That and I have been repeatedly extremely displeased with the company's corporate behavior. I think that Mozilla has proved that you can make a dent in the IE market share without resorting to lawsuits. And, when the EU made the reasoned choice to force Microsoft to add the browser ballot box on Windows 7 (which was a good idea), Opera's CEO still whined... I'm sorry... Learn to compete and shut up.