In this question, Moderation controls for Public Chat Rooms, balpha says that moderation flags can automatically ban a user and remove a message. I'd like to know exactly how many flags are required, because I've seen chat entries accrue a good six or seven flags and remain just where they were and the owner carry on.
These are the current numbers ("current" because they can obviously be changed, but there aren't any plans to do so; they have been like this for a while):
The threshold is six, meaning the net flag count of the message has to reach six. This means the number of flags (both manual flags and "valid" marks) minus the number of counter flags (i.e. "invalid" marks) has to reach six.
We also take into account the number of people who have decided not to vote either way (we call this a "not sure" vote), under the assumption that if many people see the message, but don't think this is obvious enough to be a flag-worthy message, it can't be that bad.
The "not sure" votes are taken into account with a ratio of 1:5 (and rounded downwards); in other words, for every five people doing nothing with the flag, we deduct one from the net count.
Also, a single flag or "valid" mark from a moderator will result in instant removal and auto-suspension (similarly, a single "invalid" mark from a moderator will dismiss the flags).