The FBI Director has issued a formal statement outlining the findings and his decision not to recommend prosecution. An excerpt:
Although we did not find clear evidence that Secretary Clinton or her colleagues intended to violate laws governing the handling of classified information, there is evidence that they were extremely careless in their handling of very sensitive, highly classified information.
For example, seven e-mail chains concern matters that were classified at the Top Secret/Special Access Program level when they were sent and received. These chains involved Secretary Clinton both sending e-mails about those matters and receiving e-mails from others about the same matters. There is evidence to support a conclusion that any reasonable person in Secretary Clinton’s position, or in the position of those government employees with whom she was corresponding about these matters, should have known that an unclassified system was no place for that conversation. In addition to this highly sensitive information, we also found information that was properly classified as Secret by the U.S. Intelligence Community at the time it was discussed on e-mail (that is, excluding the later “up-classified” e-mails).
Update: More takes on gross negligence and classified material from Jacob Gershman and Andrew C. McCarthy.
[I first learned of the story this morning via a message from a friend, an attorney who'd served with an intelligence agency. He was not a happy fellow.]