We didn't co-sleep with any of our children, but they do sleep with us if they are sick so we can watch them.
Having said that, I asked my doctor about children sleeping in occasionally, and her response was: "It's only a problem if the parents think it is". She is a smart woman. I say, do what you feel comfortable with. If it helps the child, go for it.
I wouldn't want my children in my bed 365 days per year, but the occasional "sleep-in" is fine by us.
