I had a tight fit on the following and I'm a 26 yo male at about 375....
Pooh - The bar sticking out makes it difficult to get in and out.
Main Street Train Station - Turnstiles are about 12" wide and thats it! (the smallest ones i know of.) VERY difficult to get through!
Haunted Mansion - Turnstiles are tight, but could get through OK.
Teacups - small hole to get in and out of and the spin wheel is close to my gut.
Indy Raceway - The belt is a tight fit.
Space Mt - ? I hear its a tight fit, but I don't ride it.
Dumbo - ? Can't remember, didn't ride it this trip.
Magic Carpets - Belt was sorta snug, but clipped fine w/ some room.
Dinosaur! - Small seat, but belt fit ok. Extended belt fully, then sat down and fastened.
Test Track - seat is small, but belt in just fine.
Kali River Rapids - hard to have 2 adults in the double seats w/ me and still get the belt on. had to sit alone.
Soarin' - small seat w/ handles on both sides. Belted in OK.
Tower of Terror - small seat like Test Track and Soarin'. Handles on both sides. Got belt on OK.
Star Tours / Body Wars - Tight fit between the arm rests, but belt in OK.
Everest - Bar clicked in fine. Sucked it in for an extra click for a slight fear of coasters. Pretty comfortable fit.
Primeval Whirl - Tight fit w/ lap bar which comes down behind you. Fun ride!
Splash Mt - Sorta difficult to get in a out of the log, but not too bad.
Most theater seats were uncomfortable. Sounds Dangerous, Carousel of Progress, and MuppetVision 3D were the most uncomfortable I can remember. Tough to be a bug, monsters inc, norway, etc have bench seats, so its convenient.
Had no problems with anything else, but still ... being fat stinks!