Re: The Impossible Girl: Who IS Clara Oswin Oswald?!?
I think that's reading too much into the Doctor's memory lapse about the GI. Remember, most viewers of the new series aren't familiar with the old series, and the new episodes have to be made to stand on their own. Having the Doctor remember the details of his previous encounters with the Great Intelligence and explain them to somebody would've been too much of a distraction from the current story, so it had to be kept an Easter egg, a passing reference that would mean something to the old-school fans but not distract or confuse the modern viewers.
I don't think modern viewers would be at all confused as the Doctor has a habit of talking about things he's done that we haven't seen.
We've met before, haven't we?