Generally (to start the thread), back in my film days, I used to underexpose a little (to the left of the cameras meter).
Have come across writings that suggest, as digital is a different format, exposing to the right (overexpose) gives less noise as the ISO goes up. Also offers greater dynamic range and more.
This is a short read that demonstrates what I'm starting to think ......http://www.amatteroflight.com/wordpress/?p=417