A man arrested as a suspect in a mugging case has had charges dropped against the court found
an update posted to his page at the time the crime was committed; Facebook verified that the post (which read merely "where's my pancakes?") was made from an address far from where the crime was committed.
The moral of this story is: if you must commit a crime, learn some UNIX skillz beforehand and rig up a cron job to post to Facebook (or Twitter or your blog) in your absence.