Rip Ride Rocket opened with a lot of excitement but it failed to reverse the declines that impacted Uni because of the economy.
Of course, Disney parks were operating in the same economy and yet saw no such declines.
What Harry Potter has done is bring many, many people to Universal that 1) had never been before and 2) had not been in years. And what people found was not only Harry Potter but also RRR, Mummy, Simpsons, Spiderman and Disaster. A lot of people found out that it's a pretty damn good set of theme parks.
That remains to be seen. I found it interesting that none of the stories about US' attendance gains mentioned the two parks individually. While we've all heard the stories of hour-long waits for WWoHP (numbers mirrored on a daily basis at Toy Story Mania, Soarin, Test Track, etc.), I haven't seen anything which suggests those crowds have followed over to Disaster or Men in Black.
So that is how Uni is drawing 1-2 days of a one week trip away from Disney.....
That reasoning doesn't exactly add up since Disney has not seen any declines in attendance.
The most likely result is that the two parks are feeding one another. Some guests are coming to town for the Disney parks and spending a day or two at US/IOA. Others are coming to town for US/IOA and spending a day or two (or five) at the Disney parks.
I truly do respect what US has done with the Harry Potter development. It's clearly exactly what they needed. And it's easy to criticize Disney for not having an equally flashy development in recent memory. I certainly HOPE that this lights a fire under the Disney execs.
At the same time, based upon my own 2009 visit to the US parks, I have little reason to believe that the adulation heaped upon WWoHP will translate to the rest of the operation. Under-staffed attractions, surly employees, too many "seasonal" attractions, tired old licensed properties (ET, Beetlejuice, Fear Factor, JP, Twister, etc), poor maintenance, often non-existent theming (imagine the uproar if Disney had done anything even remotely like RRR at one of its parks), too many simulator-based attractions, etc. I was embarrassed to have convinced my family to plan the 2-day visit. Nearly every aspect made Disney look light years better by comparison.
I can certainly see people hearing the hype about WWoHP and wanting to check it out to add some variety to recurring Disney trips. But with Disney's ticket prices heavily weighted toward longer stays (days 4+ are virtually free), it remains to be seen how many guests will consistently pay so much more for a US/IOA detour.