A relatively recent change to the flagging system has been elimination of the flag "hell ban," in favor of a more transparent system that includes feedback.
This is a good thing.
The new system, however, doesn't seem to take into account a user's flagging history, and has a pretty low threshold for what triggers the temporary ban users from flagging.
This is a bad thing.
For example, this jerk. 2180 helpful flags total, but 3 of 15 flags since the 19th declined, and flag banned. (I'm assuming it's 3 of 12 flags on posts, and a few comment flags thrown into the mix to make 15).
The effective threshold on bad flags one can throw before hitting a ban seems pretty low, at 2.5 (must have >= 10 flags, and >=25% declined), and it seems to me that a better approach would be to up the number of flags at which the system starts considering people for flag banning.
For example, if it were tweaked to start looking at 20 or 25 flags in a week (which is still pretty low, ~3/day), the lower threshold would be 5 or 6. To me, that seems like a threshold that's more in line with the intent of the new system.