The FBI seems to think that clicking on the Facebook Like button is a sign that you could have terrorist tendancies, or at least this is what they are saying in a released indictment against three people.
Facebook has always reminded me of that drunk uncle that we never want to invite to family functions because, well, he gets drunk and does stupid things. Add onto that the fact that Facebook is becoming increasingly used in the courts for things like divorces and of course the police using it to track down stupid crooks so it really shouldn't be a surprise that the FBI is trolling Facebook for "dangerous" people.
However some of their claims seem tenuous at best, which can attest to a recent indictment used to arrest and charge three men based on the men's Like button-clicking habits. From the indictment; which you can read in full here,
I have reviewed several of the social media web sites for KABIR, SANTANA, DELEON, each of whom has posted radical prom jihad content on their respective pages. Additionally, portions of the social media show that DELEON and SANTANA "liked" postings on KABIR's Facebook page as early as May 2011.
On September 17, 2012 SANTANA "liked" KABIR's post of an article entitled "A Public Talk by Ustadz Abu M Jibriel AR: The Truth of The 9/11 Jihad Operation, The Plots Of The Enemies and The Zionist Conspiracy.
Of course there is other information that helped lead the FBI to arrest them but the idea that liking and sharing questionable stuff on Facebook could lead you to being arrested to the degree that seems apparent in these documents is a little disturbing.