I have two boys, and the youngest went through a princess, barbie phase when he was 4 or so. We didn't buy him any dresses, but he found things to make do with - a bathrobe of mine, for example. We didn't discourage him or encourage him, although we did buy him a Barbie doll or 2. He even took the Barbie to preschool for show and tell a few times. Negative peer pressure kicked in by kindergarten, and he can't believe it now when he sees pictures of himself dressed up. It did no harm, but I believe it would have been harmful to not allow him that expression that he seemed to need for whatever reason.