A guy once cut up my dad causing him to emergency stop nearly giving himself whiplash, which he proceded to give the universal 'I dont like you' gesture to the guy only for the guy to do a U turn at a roundabout and follow him into morrisons carpark and knock him out My dad still made it back with a 24pk beers for my 17th bday party Since this I very very rarely make any jesture, its always better to pull over and think yourself lucky, you never know which whacko is in the other car!
As for taking licence plates and telling the police that wont do anything, only way is if a cop is there at the time as a witness, I believe there is a website for posting bad drivers on.