I'm in the middle of reading a fascinating book that I was given at Xmas called Inside of a Dog: What Dogs See, Smell and Know (great book, btw...I highly recommend it!)
On the topic of dog kisses and licking:
In the wild, pupplies like the face and muzzle of the mother when she returns from a hunt, anticipating her regurgitating her meal to them. Licking apparently stimulates her vomit reflex.
Also, in the wild, canines muzzle like and sniff to confirm who is coming to the den and also to confirm where they have been.
That being said, our faces smell and taste wonderful to dogs....salty, sweet, the garlic you ate at lunch, hhmmm! yummy smells to a dog! You just smell and taste good!
That being said, if this behaviour is allowed, it does actually turn into a ritualized greeting between you and your dog. That is, it really is just a way of saying hello!
All to say, that as long as the licks are accompanied by a wagging tail, and general excitement, its all good.