I definitely agree with Adaptation, Charlie Kaufman is almost unbearable to watch because his social phobia really hits home.
I also agree about Taxi Driver, the guy was obviously socially inept to a crazy degree. I mean, he was completely innocent when he brought his date to a porno movie, he honestly thought thats what couples did. Also, that kind of numbness and alienation he feels is something I think we can all relate to.
I don't think he had SA, but in There Will Be Blood when Daniel Plainview says "sometimes I look at people and see very little worth liking", again I think we can all relate to this to some degree.