We set up a reward chart when DS1 was 2.5 to try and get him to stop hurting his baby brother - it worked a treat so I continued using for other things as and when needed.
At the moment, he gets 1 star if he cleans his teeth properly after his bath (or lets me do it), he gets 1 star if he stays in bed at night (or at least only gets up to ask me to put his story CD on and goes straight back to sleep) and he gets 2 stars if he stays in bed completely and doesn't get up at all. Every time he gets 14 stars, he gets a reward which is now becoming once a week.
Is this too generous? Firstly, I am running out of things to give him - have now bought a supply of little paperback Thomas books so he can have one of these each week.
I feel if we make him get more stars, he will lose interest and it will lose it's effectiveness but, otoh, I feel he is getting too much.