In my last post I made the case that true old school roleplaying in the D&D flavor required 3d6 recorded in the order rolled for ability scores. Check it out if you haven't yet. It's a bit longish, but mainly because of all the lists of stats. Anyway, in that same vein I will now make the case for including some sort of a system for quirks and flaws in your game.
PC roleplaying is a very personal matter. Some have a hard time breaking out of their shells. Others don't have a dramatic bone in their body. In their mind's eye, they might clearly imagine how their PC is acting and the flair with which he says certain things, but it can be hard for some people to convey that at the table. A little note on your character sheet that Dirk the Daring Dastard, 3rd level Thief has a tendency to twirl his coal black mustache, or even better chew at the ends is a colorful addition.
Good RPGs support such playing. But it's true, quirks and flaws are not a part of the D&D core element. The game can be played without them. And good roleplayers seem to do this kind of stuff intuitively. But all too often we are loathe to linger on things that might be considered weakness. Things like, Varbatelle the Fighter is deathly afraid of cats. When she was an impressionable girl of but six years she found her mother dead on her bed. Her mother's favorite black cat Instigo resting on her chest, licking the drooling saliva off of her mother's chin. She was certain with the certainty only the mind of a child can achieve, that the evil cat had killed her. The cat had always hated Varba anyway. Had scratched at her whenever she got near. The thing was evil she now was sure. For weeks, months and years after she kept a wary eye on the beastly thing; and always locked her door when she went to sleep at night to keep the cat out while she slept. At 12 years of age she finally killed the old thing. But not without suffering a vicious scratch for her efforts. Three days later she was down with a deathly fever, red streaks rising like streams of fire up her wounded arm. The crimson scratches left by the devilish feline were swollen and hot to the touch. The heat soon reached her heart and she almost died. A month later after numerous visits from the physikers she was able to leave the bed. She was not the same however and her constitution never fully recovered. Reflecting her slightly low constitution score for a fighter.