What if there was a Web service similar to plusplusbot.com that could collate car registration numbers in the context of good or bad driving. If you spotted a bad driver you can tweet their registration number with x hashtag (possibly including location) and a positive or negative modifier that would then classify that number.

If critical mass is achieved you could have a very useful resource that could help law enforcement in finding bad drivers and encourage good drivers through promotions.

Potentially insurance companies can use this as well to find out if potential clients are good or bad bets.