I had heard hubbub that he was waiting until the end of the HBO series .. but I'm really not sure how accurate that source is either. It would be pretty epic (and potentially amazing for book sales) if he released it the day after the HBO Series Finale [talk about free publicity!].
But that would just feel dirty for those of us who've read the published materials. I had to change my original comment of "paper books" to "published materials" because I realized there are many people who are less strange than I who read, and enjoy, e-books. I am "old fashioned" and can only focus on reading paper books where I can feel (and smell) the pages!
I think I had to read a quarter or half of one of the series in e-book form because I couldn't buy it in paperback yet ... and it took me forever to get through that much ... then I found a paperback copy and didn't put the thing down! :)
I'm a paper book dude too. Can't get into reading on tablets. Nothing better than a book to get lost in. Love it!