uh What? It is and always has been one of the most compliant...
Don't get me wrong, it's far better than IE, but whereas if you get something working in firefox, it usually works as is in safari/chrome, there's sometimes little quirks in Opera.
As a relatively small userbase use Opera, it'd just be nice if it did things exactly the same as firefox/Chrome - layout, scrolling, iframes, etc etc
I can't remember specific details, but I often notice weird layout quirks, or issues with scrolling (Not well defined in any standard).
If something does need to be fixed "for Opera", it's generally only a tiny CSS change, as opposed to the kinds of structural overhauls IE will make you wrestle with.
In short, in the name of standards, I think it would be nice if FF etc did things exactly the same as Opera :)
Sometimes the one who is different is the most correct. Maybe if you satisfy Opera first, you won't have as many problems with the others.
Compared to IE? Yes. Compared to Firefox? Depends on the release schedule of both. Compared to Chrome or Safari? It lags significantly behind.
In that case you can still get one by using the "link" link to get to it.