Our son was 35 weeker and the first awake smiles were when he was about 2 months old.
He's been a little slower than his older brother to develop some skills like crawling and walking, but in the range of normal if we adjust for his age. Our pediatrician said that by 2, most premies more or less catch up. He's still small (not quite 20 pounds at 18 months!), but otherwise it's hard to tell that he is any different from his buddies who were born full-term.