I went Sunday, and of course I was present when GRRM was being interviewed(by the dutch translator of his books) and we were allowed to ask questions. He'd said several things about AFFC that were new to me:
First of all, the prologue will be different from the prologues of the previous books. In stead of one viewpoint, there will be several, from characters at different places. This prologue will be longer than the previous ones, and be divided into sections.
When he told us of AFFC, he explained the whole 5-year gap thing, and that instead of five years, AFFC will begin seconds after ASOS' ending. Well, that of course we knew already, but then he said there will be some overlap; some of the scenes in AFFC will take place before or during the ending of ASOS.
When I asked him which of the places we never saw before, he is going to show us, he said that there will be quite some scenes on the Iron Islands, and also Braavos and Dorne. I am not sure if he meant that these scenes will take place in AFFC or simply in the following books.
Someone asked (again) if he could tell us if Ned was Jons real father or not, and GRRM answered that he will not reveal it (of course) but that the whole mystery about Jons parentage will be made clear somewhere in his book, not in AFFC, but perhaps in the last book, or even the book before that.
GRRM still wasn't sure whether he would write 6 or 7 books. He still hoped to be able to finish it in six, but couldn't promise anything. He also told that writing about the Red Wedding was very hard to him. It was in fact the last he had written of ASOS; he first wrote everything that came after it, the whole ending, and only then about the Red Wedding itself.
He said that in his original plan (when he wanted to write a trilogy) the Red Wedding would take place in book one, and Dany's landing in Westeros in book two. Now he says that Dany's arrival in Westeros will take place in book 5, A Dance with Dragons.
GRRM also talked about series with no apparent ending. He said that while the Wildcards were such a series, those were meant to be so, everytime another adventure, but that when you have a fantasy-series that keeps on going, with the end getting farther and farther away, that's a bad thing. I woder if he thought about Robert Jordan when he said this. It was mostly in response to the question when his series would end.
[Note: The following is futher information Harren provided after seeing discussion concerning the Iron Isles and Dorne.]
About the overlap-thing, IIRC GRRM first mentioned that AFFC will slightly overlap ASOS(or/and some scenes might even take place before ASOS ending), and at the end he told that there will be some scenes on the Iron Isles, Dorne and Braavos, that in response to my question; I asked if he is going to show us places we haven't seen before. So the Dorne/Iron Isles thing does not necesary take place in the overlap, perhaps not even in the book, because when he answered my question I wasn't sure if he meant that those scenes would take place in AFFC, or somewhere in the rest of the series. He did say something like "quite some scenes on the Iron Islands" or something like that, which makes me think that there must be a POV sometimes visiting/staying on the Iron Isles.