This is an excellent article on Co-sleeping, the studies that support it, the studies that do NOT support crib sleeping, and why:
Cultural Influences on Infant Sleep
Written by Dr. James McKenna, Professor of Anthropology and Director,
Mother-Baby Behavioral Sleep Laboratory at the
University of Notre Dame
"perhaps no other issue has been so often misrepresented and grossly oversimplified as parent-infant cosleeping....New data from psychology are presented which raise the possibility that clinicians have overestimated the need for infants to sleep separately in order to assure "independence"from their parents......Heron's (17) recent cross-sectional study of middle class English children shows that amongst the children who "never" slept in their parents bed there was a trend to be harder to control, less happy, exhibit a greater number of tantrums. Moreover, he found that those children who never were permitted to bedshare were actually more fearful than children who always slept in their parents bed, for all of the night (17)."
... and it goes ON like that... it's very long, thorough and a wonderful article that I often mention when people look at me funny when I talk about co-sleeping!