[twobluestripes]

It looks as if this is going to be the battle of the fandoms, but I don't think the actual fans will see it that way. If a person is a fan of one and not the other, then that person could just care less. If one is a fan of both, than they are excited about both offerings and will enjoy both, as their life permits.
Also, a person doesn't go to Disneyland/World because they are a fan of Star Wars. They go because they are a fan of Disney theme parks. They enjoy the Star Wars attractions if they are a Star Wars fan, but they generally don't pay for admission just for Star Wars (that's what Star Wars Celebration is for).
However, the only reason to go to this Potterworld is because you are a fan of Harry Potter. If you are indifferent to (or, God forbid, you dislike) the Harry Potter series, than you wouldn't really want to go. It seems like it's going to be such a big piece of the IOA park (according to them, a "park within a park") that people will start to go there solely for HP (and i really don't see this happening at Disney for one or two attractions).
I really don't see this as a competition. True, if a family wants to have a theme park vacation, they will probably have to choose between the two parks, and this Harryland will prove to be quite popular, I'm sure. Disneyland will have to keep themselves up in order to maintain their clientèle, but a new Star Tours surely isn't considered specific Anti-Potter ammo.