via hitwise / searchengineland...

* On Christmas Eve, December 24th, Facebook had 7.56% market share, whereas Google had 7.54%.

* On Chrismas Day, December 25th, Facebook grew to 7.81% and Google dropped a bit to 7.51%.

* The day after Christmas, December 26, Google regained its crown as most visited site in the US with 7.33% share, while Facebook had 7.12%.

Maybe it's because everyone was snowed in and bored?