Recently I had posted what Disney's own balloon supplier had told me (via Guest Relations & Brenda Bennett) about the balloons at WDW. Unfortunately, having come back from our trip (9/29-10/8/07), I have to say that they were mistaken concerning the latex "risk".
As you can see from this picture,
while their latex balloons are encased in a non-latex "outer" balloon, there DOES remain a latex risk that is not insignificant. If you look at the bottom of the red balloon where air/helium goes in, you can see that the latex balloon (the red balloon inside the clear balloon) extends past the bottom of the clear outer balloon. When walking through the parks, especially on a blustery day (sorry, had to borrow from Winnie The Pooh), the large bunches of balloons carried by the vendors will often be blown down into your face, and those bunches can be VERY hard to avoid.
Additionally, while down there (sorry, I don't have a picture of them), I did see many balloon animals in several of the parks. Balloon animals were all made using obviously latex balloons. So, yet another potential problem.
All in all, WDW is very good with allergies, but latex they're not QUITE as up to speed on as they'd like to think they are. I'll probably be writing to them in the near future about this very issue. Of course, I'll let everyone know whatever their reply may be.
In the meantime, be safe, and Enjoy the Magic!