I bought a 90g corner tank and from doing research and the help of the people on this website i plan on making it my first salty tank. thom is right, they are a pain to light, mainly because it is deep and oddly shaped. But personally i think they are beutiful when done right. A good Metal Halide light is what i am gonna use for my salty which is good for deep tanks. And besides that you hang it high over the tank so it gives it really good lighting. So no, in my opinion i think they are fine if your doing a saltwater, but i could imagine that a freshwater would be a pain.
Almost all big lights need a fan because of the heat. But you can leave the MH
lighting bair in the air and it would be fine.