Colin's first smiles were sleep smiles, which he still does. I love holding him after he has just fallen asleep and see the cutest little grin come across his face. Sometimes, if he fell asleep while nursing he will still be attached to me and smiling.
When we were in Indiana, he started smiling here and there in response to what we were saying to him. We found (which is still the case) that he will smile more in the morning. I think we all spent so much time in Indiana trying to get him to smile... but he just wasn't that interested. Here are the first smiles we caught on camera (from my phone, so not the best in the world).
The funniest thing that he has started in the past few weeks is smiling at his toys. In his swing, he'll look at the mirror and the bees that fly around the mirror and just grin. Then the other day, when he was in his bouncy chair, I even got it on camera - he spent probably 5 minutes laughing at the animals on the toy bar... but once he noticed I was looking, just stared at me.
But rest assured, if someone other than Mike or I tries to get him to smile, it's no problem. So if you're around, just look at him with some goofy look on your face and more than likely he'll smile for you. If only he weren't so stingy with us...