Totally Freaked Out!

Please, please, please tell me there is a very rational explanation.

I went to Amazon.com to look up a book for myself. I understand why they are showing books about Paris, knitting, babies, contemporary fiction and gluten-free eating on my "home page". But, I am COMPLETELY freaked out that they specifically recommended books for my "history-buff father-in-law"! How do they know who I am giving what books to?

Seriously FREAKY!!!!