My nephew (who is 16) is mildly autistic, and he tends to take things literally. When he was younger, for example, you didn't dare tell him jokingly to "go jump in a lake," because he'd think he was really supposed to do it. He's gotten very good at recognizing (and dishing out) sarcasm, though--no doubt because in our family, he gets a lot of practice.

Some researchers believe that Albert Einstein and Issac Newton had Asperger's. And there has been a huge increase in recent years in diagnosis of various forms of autism among children in the United States.