I've just tried asking a question (well, I've just tried asking it again, as the first attempt didn't seem to "take", I probably pressed the [Post Your Question] button and closed the tab) and it seems as if clicking on the [Post Your Question] tab doesn't work.
I seem to be able to post this question on meta.serverfault. I have successfully posted a question on StackOverflow, using this browser, back in February.
The "main" symptom is that the button appears slightly grayed out and clicking on it does nothing. Is is just a question of asking a "longer" question?
Edit: I have now tried posting from Iceape and taht seemed to work fine, so the immediate worry is over. However, I suspect it would be good to know if this is a problem on the Opera side or if it's site-dependent.