By the way I feel a lot of people are naming XXXmm lens just because of its price--will you actually use it? Probably not. I can understand if you're a sports photog, but I promise you people are naming these 200mm+ lenses just because of the price. Lame.
Landscapes, birds, air shows, auto racing... all these can use long lenses effectively. I'd say 50% of the photographers here photograph at least one of these subjects.