Here is a great article on the care and feeding of histograms. Most articles just give a little short and sweet description of the little puppy. But Mr. Sean Duffy, over at SDuffyPhotography.com has quite a thorough discussion of the lowly histogram.
He goes into quite a bit of detail about how to read it under various lighting situations. Including under to over exposure, and with different subject matter, too. Nice article , give it a read right here. Here is another great link on the subject right here at Luminous-Landscape - very thorough and complete read.