I think the eyelids are too thin for me to want to poke needles into it. I've had too many surgeries on my eyes for something like that.
Also, what happens if they screwed up on the tattoo?
I don't think I'd get them on myself, but if it doesn't look unnatural for someone else, I don't think it'd be bad for them. (Heck I got eye surgery so I wouldn't have to deal with contacts and glasses every day...didn't turn out perfect but saves SO much time and I never have to worry them at all, so I can see why people would do it)
flipshawtii: I think I've mostly heard eyebrows, eyeliner, and lip liner