A lot of good advice so far. From my own experience I really think the advice that sleep training equals better sleep habits as an adult is false. When DS1 was a baby he was an okay sleeper once he was asleep, but getting him to sleep was rough. We spent many, many hours rocking or walking him around to get him to sleep. We never did any kind of sleep training, no matter how exhausting it was at the time, and no matter how much my MIL tried to push us to do it. We just responded to his cues and let him sleep with us when he needed to and fed him at night. He is an excellent sleeper now, goes to bed at 9pm without a big fight, wakes up at 7am (when we come and get him out of bed), still takes a 2 hour nap. DH on the other hand, was sleep trained by CIO from a very young age and he has pretty bad sleep habits. My brother and I both have very good sleep habits and my mother refused to let us CIO. So, just from what I've seen, I just don't buy it.
And I also think of people I know from other cultures, like some of my friends from the Middle East, and they let their kids sleep with them for awhile, but they don't all have kids that grow up to be insomniacs.