Well, it's taken him ten months but George RR Martin has finally given us an update on when to expect "A Dance of Dragons". He's still plugging away at it, but hopes to have it ready by the beginning of summer and available in the fall. There is also a new sample chapter available at his website featuring Jon Snow.
At the rate he's been writing I'd guess it's going to be about twelve years or so before he finally finishes the series. I certainly don't want him to do a rush job and not put out the best product he is capable of producing, but damn, I want to read the rest of the story already. I picked up the first book about six years ago. Eighteen years is a long time to wait to read a good story.