My natural sense is that they aren't that dangerous, depending on the child, and with the right child I'm sure they could make anything dangerous HOWEVER I remember a dozen years ago or so someone telling me how terribly dangerous cosleeping with a child is and for me I feel a lot safer with baby next to me so I researched it and while I couldn't find any actual PROOF of that being the case, I did discover that the two most frequent child injuries were from bunk beds and lawnmowers (I can't remember which was worse, the lawnmowers really surprised me!)... so despite my feelings that it really shouldn't be that dangerous, the facts, at least a dozen years ago, seemed to say it really was a major concern, more so than just about anything else apparently (for nonfatal injuries at least).
Here's a semi-recent article (from a year ago):
http://www.msnbc.msn.com/id/24895552/ the headline says nearly 36,000/yr treated for injuries, however the article goes on to say "Plus, the new study analyzed only injuries that were treated in emergency rooms, not those seen in clinics or by private doctors or those that were taken care of at home.
'We may actually have underestimated the number of injuries that occur,' she said"