Optimizing for browsers....
I seriously doubt if Opera has enough of a following for the vast majority of web sites to write code and optimize for the browser. It's probably enough of a task for most web site developers to have to make sure their sites work with the major players, IE, Firefox and Netscape.
I've used Opera off and on for many years... Mostly off the last few. It's always been fast, but not necessarily intuitive. I don't know what it's like now, but it was a big change to use it from Internet Explorer a few years ago. It's been impressive for speed and light code, but always at the back of the pack.
It's the underdog's underdog in my estimation and not worth the effort to keep up with it's differences. Frankly Firefox changes versions and code far too often for my liking. I often jump back to Internet Explorer, but they too are cranking out changes very fast.
I may look at Opera again, but I feel there will always be a large number of web sites that just won't step up to optimizing for the browser. Most likely forums will be on that list.