My bookselling friends tell me that December is the big book-selling month of the year. (These Census figures show even bigger spikes in January and September, but these are from textbooks, which make up a really big chunk of the total book market.)
And indeed, sales of How Not To Be Wrong shot up in a very satisfactory way during the holiday season; according to Nielsen BookScan, the book sold more copies in the Dec 15-21 week than it had any week since the first month of release in June. The book also rose up the Amazon rankings; having settled in in the #1500-2000 range for a couple of months, it popped up to around #700, about the same level as August, and stayed there for two weeks. Two days after Christmas, pop — immedately back down to four digits. The increase in ranking suggests that How Not To Be Wrong was unusually popular around Christmas, even relative to other books.
One thing I don’t quite get, though; the Kindle edition also got a notable rankings boost in the second half of December, though a bit smaller. Where is that coming from? Do people buy books for other people’s Kindles as Christmas presents?
Quomodocumque 
“Do people buy books for other people’s Kindles as Christmas presents?”
Yes! My wife has several ebook-only books on her wishlist.
Also, I bet lots of people get Kindles (or compatibles like the iPad) for Christmas and then immediately purchase some e-books to go with it. Also, it’s one way to spend an Amazon gift card…
Another effect could be if people take time off at Christmas they load their kindle with holiday reading. Not sure about the US, but here in Australia, because it’s also summer Christmas is the holiday season. But taking leave on top of the high holidays appears to be popular in the UK, and other northern hemisphere spots too:
http://www.independent.co.uk/extras/big-question/the-big-question-are-we-taking-too-much-time-off-over-christmas-and-the-new-year-767701.html