Callum has mild autism. He was already under a neurologist when he was diagnosed so we didn't go to the docs with a list of his symptoms or anything - the hospital monitored him over a week and said he's got this, this and this.
The only symptoms we find difficult are his social skills - he doesn't understand other people, if he hurts someone, he doesn't care / realise / understand, and he also finds it difficult making real friends. We all notice social cues which tell us what is and isn't acceptable, Callum doesn't, so whilst everybody in the school knows him and likes him, he doesn't actually play with anyone. His lack of fear / danger combined with his tendency to go overboard with things.
He's very repetitive, which doesn't really cause any problems, but at 2am when he's been making chicken noises since 6am the previous day, it tends to get a bit annoying.
Like missac said, everybody has certain autistic tendancies as part of our personality. The internet has a dispropropionate share, because people who find it difficult to socialise in real life (classic sign of autism) find it easier 'online'.