Ego Docs has strong words for Opera Web Browser when trying to create a new Presentation:
Sorry, but this browser does not support web presentations.
Usually, this is written the other way around to say the application does not support this particular browser. But, in this case, Google words it as though Opera does not support Google Doc's presentation application.
It seems to me Google should be a bit more specific in its accusation though. I know for a fact that Opera does support numerous forms of 'web presentations'. The truth is that Google's specific implementation of web presentations does not work in Opera.
Ok, Ok, I admit maybe I am reading too much into this. I tend to be a bit over zealous at times when determining intentions behind words.