I myself am set as a donor. My way of thinking is, why should I hog my organs after I'm dead? It's not like I'll be needing them for anything. While maybe some religions might see it as desecration to remove my organs, I'd see it as selfish and idiotic to just have them rot inside my already decaying body instead of giving them to someone who's still alive, breathing, and has a chance to live the rest of their lives out.
Pun line: What will happen to my body after death? It'll probably start to smell...really bad.