Extensions have a ways to go with Opera. I am hoping v12 changes the APIs to make them more usable. They are good, enough, but could be better when compared to chrome or firefox. I am not a fanboy of ANY product, I am just willing to recognize the shortfalls in a product. No product is perfect and opera is decent, but there are still compatibility problems with some major sites.
Opera, on various systems I've tried it on, has long "delays" when opening menus, clicking links, or using other features of facebook. Google plus does not get update notifications, allow you to access the top right menus without third party code injection (even that is ify). There are more sites I could list but I do not remember them off the top of my head since I haven't had opera installed in a bit. Yes, LP/RF work, but Opera continues to experience issues compatibility problems with many pages. They still have the mindset that website developers are out to get them, when in reality, I think Opera should make their browser work like every other browser does in regards to rendering.