I definitely don't think the monroe is very cute. I think the reason it looked good on marilyn monroe was because it was a natural beauty mark and even though it seemed weird, she was so graceful and poised that she never acted like it was a flaw. That confidence was what made it seem attractive. Putting one there voluntarily doesn't fit any of those same reasons, so I think it just looks unusual.
As for general facial piercings on girls, though, I think nose and eyebrow look great.
i haven't really found any attraction to girls with the monroe pierce or any other "beauty mark" mainly because most the girls I have known to do them really look better with out it. I'm one of those guys who thinks girls look fine without makeup and look best without tattoos or piercings.
but then again that's my opinion. I don't know what you look like with it or without it so you may be just as beautiful with it as you are without it.