The info in the link below is a MUST READ for anyone interested in D-SLR photography. Dave, a local photographer here in Japan, posted some excellent info on his blog and I think it would be a shame not to share! I wish I had had a breakdown like this when I was first switching over to manual on my SLR. I hope some of you find this useful! Even as someone who shoots almost solely in manual, it's still nice to see this info broken down so simply.
While you're there you should check out some of his other posts. He does a tremendous job at capturing Japan on a daily basis!