It bothers me how Google undersupports Opera and how much effect it has on usability of their services. Plus is not working very well, for example the translation of link inserted into new stream entry does not work as in other browsers, Picasa is just lame in it, extensive usage of Javascript in Gmail can make the responses slow sometimes... Opera has to update the browser.js to make it work at least somehow.
However I love the way how can I customize Youtube with extensions or usersrcipts, how add blocking works (btw here's a generator for common ad source in many formats, one of them is Opera's urlfilter.ini here
http://pgl.yoyo.org/as/ It completely different experience to surf the web with ads blocked or not.
Microsoft services like Technet and MSDN forums are also crippled in Opera but I know it is not Opera's fault.
Opera is unbeaten in working with lots of tabs - try working with 30+ tabs in other browsers and compare the speed and responsiveness of the user interface. Opera link is just great - there is simply no need for services like Readitlater on Instapaper if you have Opera Mini or Mobile on your phone / tablet, the bookmarks just sync there too. If it has problems it is most probably Flash error or situation where too many extensions and/or userscripts are processing the page.
I miss just better session manager preferably with syncing via Link.
