My son, now ten, was a great baby. Very easy going, very happy, and until about 15 months, was a tease with any waitresses when we went out to dinner. Quite the flirt! He didn't do eye contact very well, and he kind of arched his back somewhat when we would hold him, but otherwise, a really great baby. After 15 months, though, he began to get really quiet. He acquired speech, but it was slow in coming (he didn't speak slowly, he just didn't acquire that many words), and by the time he was two we could see that he didn't relate to us or other people the way most kids do. It was a very obvious line of demarcation between what he was prior to 15 months, and after 15 months. And it had nothing to do with an MMR shot, because I inadvertently forgot to get him one (we moved right when he was around 15 months, and I thought I had gotten the MMR shot for him when I actually hadn't).
Kris