I've been playing with my Canon XTi and noticed very quickly that it tends to underexpose by about 2/3 of a stop. Of course you can correct that in PhotoShop or other image editing software - but that pretty much guarantees more noise.
I've taken to doing several shots and increasing the exposure until the histogram gets as close to the right side as possible without going right up to the edge. This gives me the brightest possible image.
Also consider that sometimes specular reflections (shiny white spots on edges of things) don't have to be within the histogram so you can discount that if its running right up to the right edge.
From what I understand, some Nikon dSLR's will overexpose, so you might pull back the exposure until it makes a nice histogram.
If you're wondering what I'm talking about - click on the "BestPhotoLessons.com" banner at the top and read up on histograms.
