Facebook changed your e-mail address, here's how you can change it back
 

Today, Facebook was kind enough to replace the e-mail account listed on your profile with the @Facebook.com e-mail address it provided you with awhile back. Wait, you didn't give Facebook permission to make the change? No one did. Not cool, Facebook.
http://howto.cnet.com/8301-11310_39-.../?tag=mncol;1n