Sorry that your pictures didn't turn out -- I've never had a problem with disposable cameras. In fact, I have had great results with them. There are so many variables that could have affected the quality of your photos -- from the quality of the camera itself, to the possibility of light leakage (cracks in the camera body or opening the camera), to x-rays ruining the film, to incompetency at the photofinisher. We can't eliminate the person pushing the button either. I have come to realize over the years and thousands and thousands of photos shot that, for the most part, I'm the one to blame for my bad photos. In many cases the lens on a disposable is quite good for the price paid and there are some disposable cameras that I believe work much better than "real" cameras or digital cameras.
Even the best camera won't give you the results you want if you don't necessarily understand how it all works. We're talking light here. The first step to getting the great shots is understanding how your particular camera or the film used will react to the light. Some of the more reputable camera shops will offer basic owners' courses to give you the resources to make the shots. Check out this month's issue of Consumer's Report magazine. While the DIS folks can be a wealth of info -- I think the results of the intensive testing at Consumers Union are somewhat more definitive.
Just a few bits of advice of things I often see at places such as WDW:
1. Don't try to take a pic of Cinderella Castle (or anything big, for that matter) with a flash at night. It won't turn out. Your tiny flash can't illuminate the entire building. Use a tripod with high speed film or with your digital cam.
2. Don't try to take a pic of someone standing in front of a place like Cinderella Castle at night with a flash. You'll just get a nice pic of someone standing there and you won't necessarily see the building in the background.
3. Don't try to take pics of fireworks unless you have a tripod and turn off your flash. It doesn't help.
4. Turn off the flash when you try to take a pic through glass -- such as at Living Seas.
5. Buying a camera is just like buying a house -- buy the most camera you can afford with the least amount of money.
6. Take your time -- best of luck.