Facebook profiles — “info” and “wall” pages — are often viewable to others in the same network, providing historical and real-time intelligence for your investigations. All this can be done passively without a special request to “friend” them. I have a link (named, Adversary’s Social Network Profile – Admissible in Court) on my social bookmarking site to an article that discusses the admissibility in court of webpages and content from social network profiles.
Admissibility also concerns public records, publicly available personal information and violations of privacy. There are legal and ethical issues that arise in methods of information gathering. Some techniques may be acceptable in an investigation to gather background or investigate fraud that should not be used in litigation. That said, there are ways to passively view content that takes advantage of technical glitches in applications and of a users privacy settings. One of the people I follow on Twitter (see my sites at twitter.com/PIbuzz and twitter.com/ThompsonPI) is twitter.com/BrettTrout. He provides a Google query to obtain private notes that Facebook participants have added to their sites. I have a link to this at my Twitter pages. If you want to search for notes on a particular user’s profile, just insert her name in the search bar as part of your query.