Freefly. I've just taken a pretty good look at your site and it could be related to your heavy use of affiliate links. Amazon store pages won't help either - and you have quite a few. Like this for example:

http://www.all-things-photography.com/camera-bag-store.html

Then there's the directory.

Essentially I can identify a bunch of things about your site which may cause problems given the recent algorithm update.