Websites with Facebook widget where visitors can join the fan page ( example: Blackberry ) , could have a gold mine full with valuable information they could present to their advertisers.
I don't know whether Facebook shares this data with websites owners .
Just imagine the fan base of few thousands people who clicked '' like '' button. All these users share their personal information with Facebook and if shared, website owner could knew exactly their audiences.
No need for website owner to post polls, user surveys etc. The information is stored with Facebook.
The problem is that Facebook won't share it with websites, I presume. They will use it to drive advertising through Facebook platform.
Remember, Facebook’s advertising platform gives advertisers the ability to target their advertisements to Facebook users based on their demographic and psychographic information – including their likes and preferences.
Thought provoking article by Ed Dale.