My DH proposed at the Magic Kingdom. He was originally going to propose during Wishes Fireworks, but some really annoying kids ruined the moment. It all worked out though-fireworks are romantic in theory, but can also be loud, crowded, & impersonal.
He ended up proposing in from after park hours, in front of the castle entrance, during the "Kiss Goodnight" (not sure if they still do that?). We were all alone, except for a custodian off in the distance. For us, it was perfect!