While there appears to be hundreds of references in a Google search about dishwashers being more efficient than hand washing, all those sites seem to be merely cloned version of the same comments (usually with plenty of embedded links to buy or install dishwashers). Just like the repetitious claim that the average dishwasher uses 15 gallons of water. But I finally ran across an article in the UK Guardian which also questions the practical comparison of bad hand washers to super efficient machines.
You can read that article here: http://www.guardian.co.uk/g2/story/0,,1605710,00.html
And then there is a nice little story and study done by Ask Pablo. He has all the numbers and details including the name and model of the dishwasher he used in a more realistic setting. You can find his story here:
I'm not out to kill the dish washing machine. I really just want people to be more efficient about their choices and how they use them. We won't always have the time to be more efficient. Nobody is going to try and tell us that driving a car is more efficient than riding a bike. We know it uses a lot of energy which translates into more pollution etc. But there are times when we can make a better choice and we need to exercise that option.