I am an organ donor (how could I ask for someone elses when I won't share mine.... My opinion though) but I know a lot of people who aren't. My mom, for instance, isn't a donor. She may change it soon... but it's just something that never "spoke" to her until she was directly affected. A friend of the family died a few years ago and she wasn't a donor (she was 17) because it felt wrong to her. She had complications with a surgery and beforehand made her wishes clear about everything to her parents. The doctors ended up taking her eyes anyway and their still trying to legally sort this one out.
Anyway, all that being said, even though I'm waiting for lungs, I understand why people wouldn't want to donate. Maybe that's because of what happened to that young girl's family though...