Spectra senior editor Anne Groell, when inevitably asked about A Dance with Dragons, had this to say:
"We're hoping to have a finished manuscript by Christmas. He's told me he has five chapters left and bits of each chapter are done. He really wants it done by the end of the year. We really—I mean really—want to announce the pub date in January."Given that much of the manuscript is said to have already been 'locked' (edited and ready to go, in other words) it seems that a publication date in 2011 is definitely a possibility. While it looked at one stage that the book would be even longer than A Storm of Swords (1530 manuscript pages), it seems likely to be shorter now as some chapters have been moved to The Winds of Winter instead.
It'll be interesting to see how the US and UK editions are published; to my knowledge, A Storm of Swords was released in one volume in the US and in two volumes in the UK (in paperback), so a repeat of this is certainly possible.
Another issue that remains murky but will become clearer with time, is whether the series will exceed seven books. GRRM has insisted that he doesn't want to exceed this number of books, but with chapters being shunted from A Dance with Dragons to The Winds of Winter, it's possible this will also happen with chapters being moved from The Winds of Winter to A Hope of Spring, which if course will eat up space in the final volume for fresh material. Only time will tell whether this will become a problem.