I'm 6'2" and weighed 360ish the first couple of times we went to WDW as a family. Didn't have any problems with any rides. Rode pretty much everything except Dumbo, Astro and Indy Speedway. Rode all the thrill rides at the time Space Mountain, Big Thunder, Splash, RnR, ToT, TT, Dinosaur, Mission Space. Not a single issue. I will say that the Pimeviel Whirl, while I fit, wasn't the most comfortable. Because of the curved nature of the reide vehicle and my height, I had to turn a little sideways, which caused me to spill over the bar separating the seats. That was the only ride that was uncomfortable as I recall. Also, an earlier poster was correct on the Roller Coasters @ Universal, Rows 3 & 6 have a bigger seat for bigger people. Didn't have any problems there either, although Mummy wasn't there when I was that large.
I have since gotten to 280 (hopefully still have further to go) and rode the Mummy then, didn't have a problem.
WDW is great for pooh-sized people. Have fun!!!!!