This is the first time either of my children has ever chosen to go to bed. Don't get me wrong, I don't have to strongarm them off to bed every night and tie them down, but I generally have to convince them that it's Very Late and they must sleep.
Ok, I think DS2 is having a growth spurt or something (wet cough, runny poo, lots of swimming, very hungry, so god knows, really), but just the idea that he might notice when he was tired and ask to go to bed, rather than, say, getting more and more cranky and having a giant tantrum, is a great improvement.