I personally have let both my sons sleep with me since the day they were born. My oldest son, who is now 12, when he turned 4 just said to me one day "I think I am going to sleep in my own bed tonight" and has been there ever since. My youngest son, who is now 6, well, I am having a little trouble kicking him out. He does good falling asleep in his own bed, but he does eventually wander his way in to my room at some point durring the night.
When he was an infant I read a lot of information about co-sleeping. My own physchiatrist and I had a long discussion about it, and in most every part of the world, except in the west, babies sleep with thier mothers for at least the first year and sometimes later. He and I both agree that it seems barbaric and cruel to take a newborn, that has been lving inside of you for 9 months and then put them in an isolated, dark room with no one. It was so much easier to nurse at night, I slept better knowing he was right there, he sleept better because he could feel and smell me (remember babies know their mothers scent). My husband didnt really seem to mind, if we needed some time to yourselves, we put him in his bed, and when we heard him wake up, one of us would go get him.
Now back to him being 6 and still with me, the sad thing is that when he in not there, I wake up several times, looking for him (I got so used to his restless sleep kicking that when I go undisturbed it wakes me up).
I found this article and altough yes it could be biased, it has some valid points.
http://www.babyreference.com/Cosleeping&SIDS%202005%20Review%20of%20the%20Studies.htm
Mothers who worry about rolling over on top of there baby. My personal experience is, no matter how deep asleep you are in, your natural mothering instinct will always be one, even now as my kids are older, if my oldest son caughs in the middle of the night from his room on the other side of the house, i can hear it and immediately wake up. I dont have any exact statistics or facts, but from the stories I have read, parents who have rolled over on thier kids, seems like a lot of them had other factors involed, there were on drugs (presecription or other) or had been drinking.