I don´t know if this was said before (I don´t think so), but we also could see Dewey´s fondness for music a long time before he officially became a genius. He always liked to dance when he was alone. I think that´s really cool, because in Humilithon (the second episode of the 4th season, so a long time before this became an important thing about the character Dewey) we could see how talented he is.
This is a very small detail now, but I think it´s funny that Reese always was supposed to be kind of a coward, since this stands in big contrast to his tough image. He always was the first one who tried to escape when there was a dangerous situation (Carnival) and you also could see it a bit in Zoo when he threw the goat into the cage and ran away screaming.
There also were some other moments which I can´t remember right now.
@Garbage kills Megan:
I´m not sure if Reese is supposed to be really vain. Only thing I know is that he´s a little obsessed with his hair (Hal´s friend, Goodbye Kitty). There were some references to it, though, e.g when Jessica said that he cares so much about his body and stuff. But that doesn´t necessarily mean he´s really vain. I don´t know if this is real vanity, but in "Hal coaches", when Malcolm became obsessed with the computer game, he gave Reese´s character 0 for hygiene. Maybe he just did it because he thought it was fun, but in Funeral we learned that clothes which had been worn by Reese tend to smell like wet dog.
I think if Reese was supposed to be really vain, they would make him take showers all the time and stand in front of the mirror instead of writing in jokes about his missing hygiene.