I don't believe in any sort of anonymous "rat on someone" program for the exact reasons stated here. They can be used for petty vengeance. If you are going to rat on someone you should be required to give all of your personal info. just like when you file a police report. That way if you are LYING just to f$#k someone over because you don't have the guts to handle your own business, YOU can be prosecuted for filing a false report.
I pull over all the time for people who want to go faster than me as it is not my job to regulate the speed limit (and I drive a 240D), but it would never cross my mind to file a FALSE report about someone just because they pissed me off. I might have a word with them if I see them in town, but thats about it. After years of road rage I have found that living well is truly the best revenge.