Nothing really, people come in all shapes and sizes. Some guys like tall girls, some guys like short girls, some like girls somewhere in the middle, others don't really care what height she is. Some don't like being shorter than a girl, others don't care as long as she is shorter than he is, others like a woman who towers over him!
It really depends. Tall people have a certain grace and presence.
depends on the guy. As an adolescent got the crap beat out of me by an older tall girl. Now I am 6'2 so a 5'11 girl is nice. some girls clothing really flows nice on tall girls. This is not a dig a sorter girls. I like them all. but you asked.
I'm 5'10" and never had any issues. Some guys feel intimidated/emasculated, other don't give a f***. More tall guys are comfortable with it than short, but I know some average-short guys that don't care either.
Honestly, it's usually the girl who is more bothered by height than guys.
I'm 6ft and recently went out with a guy A LOT shorter than me. He didn't really seem to care, but I felt so self conscious all the time! It depends on how confident the guy is and what gets him going I suppose :)