How clean is a dog’s mouth?

We have all had a dog lick us at one point in time. Some think it is gross while others take it as a sign of affection and your dog is just kissing you. We all know dogs will pretty much lick ‘anything’ so I find it hard to believe their mouth could be sanitary.
I tried to google about it but I get mixed theories on the subject. Some say they are clean and can even heal a wound you have, while others say their mouths are not 'sanitary' due to the diseases or illnesses you can get from a dog bite. I would like to know what you think and any web-sites you might have that back up the theory dog’s mouth are indeed clean and we won't think ‘eeww’ when they lick all over our faces. :)