I just found out this 'Applications may be able to access a limited set of information about you through FRIENDS who opt in to other applications.'

from this http://www.news.com/8301-10784_3-9854409-7.html

It tells you how to edit your privacy settings for applications which I hadn't noticed before: Privacy -> Applications -> Other Applications....a user who has yet to discover the preference page is essentially sharing their entire profile by default.

As someone who likes the ease of facebook to keep in touch with real friends but who sets the privacy settings as high as possible, I find this automatic opt in system intensely annoying. I don't add applications for a reason, I don't see why just because my friends do some third party can access my details.