I'm sure almost none. Those of us who regularly post on these threads are WDW obsessive. We know every little detail. However, the overwhelming majority of the public (and typical WDW vacationer) has no idea. Ask people, "What do you think of the Fantasyland Expansion" and watch their blank stares. Meanwhile, most annual WDW vacationers are not going to cancel one year's trip so they can do two trips the next year after FLE is open.
WDW attendance has been impacted by WWOHP. Even the casual vacationer knows about the "Harry Potter" commercials for the "Harry Potter land" and wants to check it out. For those with plans to visit Orlando, they are taking days out of their WDW vacation to visit Universal.
Attendance would be considerably worse if it weren't for new vacationers from Brazil and Argentina. Per the conference call, it appears TWDC has had a successful marketing campaign in those South American countries that have greatly helped WDW attendance. It's a risky move since only a portion of those populations can afford flights, tickets, hotels, etc. to make the trip to Orlando. Without adding a new land soon, it's unclear to me how TWDC is going to get these vacationers to return to WDW. Give it about 4-5 years for that well to run dry. Attendance also seems to have improved from the U.K. The U.K. had a really strong attendance 5-10 years ago but was hit hard by the economy. It looks like U.K. attendance is rebounding.
Given that WDW attendance is down "modestly", coupled with the increased attendance from Brazil, Argentina, and the U.K., it seems highly likely that U.S. attendance at WDW is down significantly.