There are plenty of links that reference several studies done in this area. Here is a link that lists several:
http://www.geocities.com/maggi19/sex/cohabitation.htm
In turn, I just need to ask....do you have any studies that show co-habitation before marriage is an actual benefit?
EDIT: Apparently, Formaldehyde is some anecdotal proof of the cohabitation point. And to be fair, I am anecdotal proof of the opposite: my wife and I lived togehter off and on a couple of times prior to getting married (a result of her dad trying to break us up a couple of times). Living together did cause some unintended problems down the road, but we got through that and other issues we had. We celebrate our 25th wedding anniversary next month. We probably have done about every single wrong thing there is to do in a marriage, but somehow its worked out ok. Have to give God the credit for that, not us.