Technically, nothing is too long as long as you are proficient on them. Big mtn pros ski 195's that are stiff as hell and have a lot of surface area. Skis that are as tall as you is just a general rule of thumb. Seth Morrison doesnt measure his 'coolness' by the length of his skis, they are long for a reason. In the park they ensure an easier landing, but take away from spinning.
Big mtn riders decide length based on ability and function. Park riders do this to a lesser extent. A small number of park riders pick length for bragging rights, and this is a vocal group, so you dont always get a balanced explanation. I believe that skis that are about the same height as you work very well for big mtn and park riding. If I was strictly a big mtn rider I'd go longer, vice versa if I was strictly a park rider.
'I would be embarrassed to constantly complain about my life considering all the freedom and opportunities we have today. People that can't find anything they enjoy in life simply aren't giving it a real try.' ~Nick 311