My APBT is a big time mouth licker, he won't lick you anywhere else but your lips. If your face is anywhere near his, be prepared to put your hand over your mouth. I hate it, but that's just how he is.
My Yorkie/Maltese mix is an ear and eye licker, little weirdo.. If he's excited, the first thing he'll go for is your ear, and if you pull him away from that, your eye is next. He only tries to lick you on the mouth if you make kissy noises.
I don't exactly let them do it, but I tolerate it to an extent, and work around it.