Just subscribe to Facebook today, as it seems everyone is on Facebook.
In the profile page, you can select your sex and the one your interested in. If you don’t look closely, you click on « Men » and your profile is listed as Men interested in « Men », which is of course possible, but not in my case.
In this case, my point is once again on usability. Why would you put a drop-down list and then checkboxes, for the same type of question?