Why do dogs lick people?

"Dogs lick people's hands for different reasons, but generally, they do it out of love"

http://dogcare.dailypuppy.com/dogs-lick-peoples-hands-2630.html

Licking is an instinct present at birth,a submissive gesture,
they like the taste of an owner's salty skin, and licking releases pleasurable endorphins which gives dogs a feeling of comfort and pleasure and it relieves stress.

http://animal.discovery.com/tv-shows/its-me-or-the-dog/training-tips/dog-licking.htm

Puppies pick up licking from their mothers. The moms lick the puppies to keep them clean. Dogs use licking to greet, to convey affection and protection. Pups may lick an older dog to show respect. Amount to licking depends on the dog's personality, level of training and overall demeanor.

http://www.aboutfamilypets.com/why-does-your-dog-lick-you/

In addition to the above:

"Your dog is hungry. Dogs sometimes use licking to communicate that they are hungry. Puppies lick their mothers' lips to stimulate a regurgitation reflex so they can eat the food their mothers vomit. Like their wolf ancestors, wild dogs lick the pack leader's face as a way of begging for food. If your dog licks your face around feeding time, he may be letting you know that he is ready to eat."

http://pets.thenest.com/dogs-lick-humans-faces-5892.html