PJF's Pages - Journal - Dark Stalking on Facebook
http://pjf.id.au/blog/?position=590

What makes this all rather chilling is that I'm doing all of this via the application API. If your friend has installed an application, then it can access quite a lot of information about you, unless you turn it off. If your friend has granted the application the read_stream privilege, then it can read your status stream. Even if a friend of a friend has done this, and you comment on your friend's status entries, it's possible to infer your existence and retrieve those discussions through dark stalking.

Most recently, I've been able to obtain status feeds, even for users who have very tight privacy settings, although I had to tweak my own application's privileges to do so. I don't know how far into the past these go, but they also come with likes information, and comments. This gives me a wealth of information on the strength and types of relationships people have. A person who comments a lot on another user's posts probably finds that user interesting. If I descended into keyword and text analysis, I may even be able to determine how they find that user interesting.

Programs to pull info out of facebook accounts

the information available to people via facebook is amazing....

How I became a Foursquare cyberstalker

How I became a Foursquare cyberstalker | Technology | The Guardian

Privacy advocates fear that Foursquare, along with other geolocation apps such as Gowalla and Google Latitude, are vulnerable to "data scraping", namely, the sophisticated trawling and monitoring of user activity in an effort to build a rich database of personal information. The big worry, say critics, is who might get to make use of this information.

How I became a Foursquare cyberstalker