I've had my eyelids licked before and I really liked the feeling. It's not hygienic/safe to let someone lick your actual eyeball, though I know people do it anyway. The reason for this is because your saliva is filled with bacteria that would have a field day in your eyes if it could. This is the same reason why you're not supposed to use spit to clean your contact lenses.
Google: saliva contact lens
http://www.eyechange.co.uk/eyecare1.htm
"Don't use saliva to wet or clean your lenses -- this is teeming with potentially harmful bacteria. It is not true that your own bacteria are safe."