I like using Drop D to create a mood. D minor is the saddest of all keys, right? Well, if your in drop D, its cooler to play in that key, because you have more D's to pick from, it creates a mood, because its sadder and darker, its more convenient than dropping the whole guitar for that note range, and it allows for totally awsome chord voicings that you cant reach in standard tuning.
Its like TheDirt said, its only bad in the wrong hands.