In case there was any doubt: Yes, the New York police read blog comments and they will bust you for making threats on them, as they did a Gothamist commenter this week. According to The New York Post (via Daily Intel), cops arrested 49-year-old Richard Strauss for threatening New York Police Commissioner Ray Kelly in the comments on a post about the NYPD's reported spying on Muslims. The comment, written under the handle "Ladder 157," is alleged to be by Strauss: "A well placed round of 7.62 ammo to his thick skull would work quite well to eliminate the threat that he poses. All New Yorkers should aim their sights (both figuratively and literally) on this piece of excrement."
New York has had laws on the books against threatening people on the Internet since 1999 (it's considered aggravated harassment). Of course, people say awful things online all the time, constantly telling one another to go die in a fire. But the NYPD's understandably sensitive to this kind of thing. Besides, Ladder 157 did literally ask for it: "Come get me Kelly if you have the balls and I don't mean the ones you suck on."