Here in the UK at least, people are only diagnosed with disorders like Asperger's if there is significant problems in their daily functioning. Some people shop around online looking for things that are 'wrong' with them when there is nothing really wrong at all.
Okay, here are some extreme examples, but: if you have unusual difficulty in finding a job, if you have real problems communicating that leads to misunderstanding, isolation, and to a certain extent if you lack emotional 'intelligence' and exhibit some symptoms of cognitive dysfunction, if your performance at school declines the older you become, then you more than likely have a disorder of this sort. I saw a show on the BBC where several people with Asperger's were profiled. Because it was for TV their symptoms were very obvious. One guy met up with a girl he met online, who also had an autistic disorder. When they met at the cafe they both sat at the table, looked at the floor, and said absolutely nothing to each other for five awkward minutes. The girl carried around a set of cards with her with faces printed on them, which she used to express her emotional state. It was 'good TV' but not all autistic people are like that.
For many years doctors said nothing was wrong with me and it took a near total nervous breakdown at age 26 before they took me seriously. Now I have my diagnosis but no cure.
To be honest it's not something you want to have. People often say things like 'Oh look at Bill Gates, the richest man in the world, he probably has Asperger's, look at how nerdy he is, what a computer genius he is!' and so on. But the reality is that people overdiagnose and misdiagnose especially in the age of Wikipedia. A disorder by definition means a PROBLEM, outside the scope of problems that 'normal' people face.
The sad fact is that life for a lot of autistic people can be one long, lonely journey that has little meaning or love.