I am spooling out my imagination to try and see how a vigilante 'shame on you, bad driver' system would shake out and a few things pop up.

My first thought is that the signal to noise characteristics might make it useless as a tool which could in any way be used to 'correct' bad drivers.  I immediately think of the 'nosey neighbor/busybody<-->malevolent axegrinder/griefer' personality types who would flood such a system with tattle-tale reports aimed at every minor driving slight they saw in the world around them because it made them hatefully happy to stick it to those who 'deserve it' in a world where 'everyone's an asshole except me'.  Then there's the straight up 'I just don't like that guy/she turned me down for a date/ he got the raise I wanted/ who the hell do they think they are being happy or successful when I'm not' sort of anonymous liars who would use this as a tool in their creepy stalky arsenal of mean-spirited svengali-hood.  All of these possibilities combined with the fact that IMO most 'normal' folk get over their upset at chance encounters with bad attitudes out on the road so quickly that they would forget to report the vast majority of true offenders by the time they got to wherever they were driving make for a system that would see disproportionate representation for people who REALLY enjoy complaining and are motivated to do so.

To summarize: people ain't no good

IMO the inevitable next step in trying to make a vigilante system work is to try and control for some of the unpredictability of human observers (attenuate to get more signal and less noise).  One way would be to allow only site registered users make reports, the account would be externally anonymous but the internal administrators would be able to sift user reporting/site use patterns for tell-tale indicators of 'griefer/crank/crazy/unreliable' data generators and quietly discard/ignore their input (these idiots poison the data, identify and extirpate).
Another way to make 'vigilante's' reliable would be to take the human judgment element out of the data gathering altogether - automate the observation process by having every registered vehicle on the road broadcasting a cellular transponder signal keyed to the registration for the vehicle, the transponder not only broadcasts but logs the IDs of vehicles in proximity to the vehicle in a telemetry log which can be read back - say 30 days worth of data are saved on board.  This system could be quite sophisticated if you consider that in relatively dense traffic there would be at any given time several overlapping telemetry 'scan' fields operative and in the event of a complaint to the vigilante traffic safety board or a police post accident investigation - the relative velocities and position of all vehicles could be determined by parsing 2 or more logs and comparing readings (i.e.; telemetry captures ID signal strength at a fixed intervals which will correlate to proximity & speed) and reconstructed forensically with cool computer graphics.    

Of course when your vehicle transponder logs and cool looking computer graphic reconstruction are used at your secret tribunal to have you disappear into Gitmo because you associate with the wrong people/read the wrong books/shop at the wrong stores/go to the wrong bars/drive too fast with the music too loud - this super reliable driver safety system might not seem like such a great idea.

YMMV

"...when theft and high crime becomes obscenely obvious to even the blindest beer sucking idiot, it is always the Republicans who are in office." -- Joe Bageant

In WA state there is (was?) a program where if you saw someone driving solo in the carpool lane, you dial 764-HERO and report him. What exactly was done with the reports remains a mystery - nothing, I think - what could they do - send cops to your house "Some guy called us yesterday and said you were stag in the carpool lane, so now were going to lock you up and throwaway the key."

But the callers who ratted out people violating the sanctity of the carpool lane can tell their children about their act of heroism.

For awhile there was a band named after this program. I don't know what happened to them, but that song of theirs was annoying. There should be a hotline to report annoying songs 764-THATTUNEIRKSME. Or annoying posts - 764-SHUTUPURKEL.

... the bird at other motorists to express my lack of appreciation for their driving skills.  First of all, doing so would take my mind and eyes off the road ahead of me, and b). you never know what might be the spark that lights the fuse on powderkeg behind the wheel.  Usually, if I'm being tailgated by somebody, I will do my level best to change lanes and avoid them.  But, if I can't, I simply hope there will be an opening to the right or left allowing the tailgater to move on past me.

A lot of the trucking industry has trucks on the road with 800 numbers painted on the truck, just under a query about "how's my driving."  I have only ever called one of those 800 numbers once after I (and about three others) had been cut off by a trucker who was obviously behind on schedule and not concerned about how many people he killed to get back on schedule.  I took down the license plate number of the truck and called the 800 number.  When I reported what had happened, I was informed that I should have taken down the rather smallish serial number painted under the 800 number.  When I said I didn't know that was the number I was supposed to report to them I was told, "well, how the hell else are we supposed to do anything?"

Illegitimi non carborundum.

I just spent a little time in DC, and I was surprised at how helpful many drivers were.  I was completely unfamiliar with the area, and found myself getting stuck in blind lanes, and in every case, someone actually honked to alert me that they would let me cut in.

The roads, on the other hand, are miserable, from the condition of the asphalt, to the horrible, uninformative signage.  I wonder how many of those "bad DC drivers" are actually out-of-towners trying to deal with a road system that seems like it was designed by a sadist.

I lived in LA for a while, and the drivers there are actively malicious.  If you want to get into a lane, you'd damned well better not signal, because that's just a sign to close ranks.