The paperback version of Dance With Dragons by George R.R. Martin has been delayed. Initially, it was supposed to come out at the end of this August, but due to the hardcover being on the NYT bestseller list for 52 weeks (woot!) it's been pushed back until March 26, 2013. Please note, that Season 3 of Game of Thrones starts on the 31st, so that may also be part of it.
It will be in mass market paperback (the small size you can take with you easily in your purse or backpack), and the other paperback formats, which is as big as a hardcover...but it's 'soft' instead of 'hard'. And yes, it will include a preview of Book Six, Winds of Winter. I'll keep you updated once I find out more about the preview. I'm guessing that Book Six will be out in 2014 sometime.