Here's my two cents on the whole IOA Potterland thing:
I went to US and IOA for the first time this past April. I heard good things about Universal, and I decided it was time I checked it out.
I came away from Universal disappointed. There was simply not enough to do there, and some of the attractions I did see were just a waste of time (Disaster, ugh). Even the Hulk did not measure up, which I was very disappointed to find out because I read all the time that people love it (the launch on RNRC is way more thrilling). Ripsaw Falls was awful, bad show all around.
There were things I really liked at Universal, though. My favorites were Dueling Dragons and the Mummy. Lost Continent was pretty amazing and on par with some of Disney's best themed lands. I was pleasantly surprised by Poseidon's Fury, and Spiderman was really fun. Men in Black and Popeye were good, too.
But I digress. The point I'm trying to make is that Potterland won't really entice me to leave WDW next time I'm down there, even though I do like the books (the first two movies were pretty good, but the other ones were pretty bad). Here's why - if you'll notice, my favorite part of Universal was Lost Continent in IOA. Basically half of that land is going to be annexed by Potterland, including Dueling Dragons. The queue of Dueling Dragons is amazing (the coaster is unthemed, but still great fun and way better than Hulk), but I hate that they're going to slap some Triwizard Tournament theming around it. It will totally ruin the queue for Dueling Dragons, especially considering that the castle queue doesn't belong anywhere in the Harry Potter universe. The ride will no doubt be the same exact thing, but the queue is half of the experience and Harry Potter will probably ruin it.
Another "new" ride they're touting is turning the Flying Unicorn into the Flying Hippogriff, which will cost next to nothing for Universal. The only real additions that are worthwhile are the Weasleys' car Robocoaster ride and the Hogwarts Castle.
The simple fact that Harry Potter is going to take over the best part of Lost Continent, leaving only Poseidon and Sinbad, is not enticing me to go Universal on my next trip. And, the net expansion for Universal is only two attractions, which doesn't add enough really to fill out Universal, especially considering that I took a large part of my time there doing repeat rides on Dueling Dragons after I had done everything else.
Actually now that I think about it, US is getting that Hollywood Rockit coaster, so Universal's net expansion is three attractions. Three attractions opening close together is significant expansion, but Disney has some new experiences in store, too. We've been told by insiders that Space Mountain refurb and Star Tours 2.0 are pretty much a go, and there's still that rumor of a family coaster in Pixar Place that just won't go away.
Sorry Universal, but I won't be leaving WDW for your parks anytime soon. I live up North, time is limited down in Orlando, so when I make the trip, I come for the best. Disney still has the best rides and theming/immersion factor out there. Universal did well with Port of Entry, Seuss Landing, and especially Lost Continent in IOA, but on the other side of the park they did poorly in Marvel Island and Toon Lagoon. Disney has highly themed in all their parks, and they've been doing it since the 70's in MK. And look what incredibly themed experiences they've done since then: World Showcase, Hollywood/Sunset Blvd., and all of AK. Universal is just starting to get it.
I don't think Disney has to respond to Universal simply because they are the leader in Central Florida. Universal will see an increase in attendance when Potterland first opens, no doubt. Disney will end up benefitting from it, though. Universal may have a big draw with Harry Potter, but Disney is still THE destination resort. Disney will keep pushing Magical Express, especially for international visitors, and that way Disney will still get people in THEIR hotels. People may come to see Harry Potter, but they will spend time in Disney's parks as well, most likely Disney will consist of the majority of their vacation time, if only because Magical Express is so effective at keeping people on WDW property. Disney is aware of this, and they know they don't have to respond in a big way. Disney has actually responded already, with refurbs to IASW, POTC, HM, SSE, and The Seas. Disney might not be getting all the press attention for these refurbs, but it's only Step 1. Disney is getting their existing rides in top shape, so that Disney's classic rides will be fresh when all the new rides come, which will improve the guest experience at WDW.
I think Disney is waiting for the hype over Potterland to subside before they make their move. Don't forget WDW's 40th is in 2011, and we're hearing rumblings of great things that are happening or might happen for that big year. By 2011, Disney will have opened American Idol, Midway Mania, a new Space Mountain, and Star Tours 2.0, and that's not even counting the rumors about the Pixar Place coaster, Little Mermaid at the MK, and maybe even Beastly Kingdom or JII 4. What will Universal have opened? They'll still be pushing 4 Potterland attractions and the Rockit coaster at the Studios, and two of the "new" rides in Potterland aren't even additions. American Idol, Midway Mania, Pixar Place coaster, and Little Mermaid are actual additions. Have we even considered the possibility that many young adult American Idol fans will be flocking to DHS for the chance to audition for the real thing?
Trust me, Disney has nothing to worry about, especially after the last Harry Potter movie leaves the theaters. Harry Potter has a huge following, yes, but so do Star Wars, Disney Princesses, and Pixar (American Idol, too, but that's kind of a love-hate thing). All that being said though, I hope Harry Potter does turn out to be popular because the competition will keep Disney on its toes and the guests will be the winners in the end.
Believe me, Disney will handle Potterland just fine.