My first never slept through the night (more than 5 hours at a time) until he was 3 months of age. I had went back to work 1 1/2 months early, working graveyard, so his father got little sleep during the nights with him, and I got even less during the day!
With my second, who will be 10 months soon enough, she has been sleeping 10/hours a night since she was 5 weeks old (maybe b/c she has a different father? odd since my sons father can sleep more than my girls can haha).
I think I just got lucky, AND the second time around - I set stricter bedtime rules and routines.