There is another ongoing thread that started today that is talking about the same issue

http://www.flyertalk.com/forum/delta...-my-seats.html

If you can wait, maybe you can do SDC to a later flight so you don't have to put up with a middle seat? Heck, by SDCing you might be able increase your chances or snag an upgrade...

This sucks I know, but I have managed to weasel my way out of the middle seat everytime... Delta blocks all bulkhead seats for assignment at the airport [only the agents can assign people in those seats], so worst case scenario you can get a bulkhead seat.