I LOVE the preshow for the Muppets and will sit through it time and time again even I didn't have to. Other things do bother me (like people doing the wave before Fantasmic....I HATE the wave). There are a couple that I could skip, like the ToT when you ride the ride over and over again. The first time, I like it. By the fifth or sixth time, it gets annoying and I start to get annoying right along by reciting the entire thing along with it. Sometimes I wish that you could just pass by those as well.
My worst ones are those with the videos that loop on the tv's set up. These are more prevalent to Universal than Disney, but when you have to watch the same thing over and over, it gets to me. Really gets to me.