We actually had a Yorkie returned to the Rescue for excessive "man spot" licking. The owners were so disgusted, that they gave him up.
We were told it was an OCD thing. He eventually was placed in his forever home with people who were way more understanding.
IMO, unless he's licking some other dogs "man spot" I wouldn't worry to much about it as long as everything is healthy. My boys do it too. You may want to avoid him licking your face for a while though.