also remember it is easier(for idiots like me) to lighten a dark picture than the other way round
Also you'll pull far more detail out of an under-exposed shot than an over-exposed one, because the data is wiped out when the shot is over-exposed
this is wrong, have a read through
http://www.luminous-landscape.com/tutorials/expose-right.shtmlbasically the digital camera sensor records the most information at the bright end, and the least at the dark.
if you try to pull the exposure up on an underexposed image then you're guessing and making up data (this will make a very noisy image), if you decrease an over exposed image then you're only throwing data away. The catch is overexpose too much and you blow out the highlights (this data can never be recovered), personally I find even on a bright day mine can cope with a + 2/3 exposure bias.
Obviously you can also shoot at the 'correct' exposure, however overexposing gives you the most RAW data to play with.