For user experience type questions there is [SE.UX][1].

Programming design questions are fine on StackOverflow itself. Do keep in mind though that your question should never be a poll type of question or simply seeking opinion, IOW "Should my window have a close button at the top or bottom?" is a little open ended. *Why* are you considering having it on the bottom, have you done any research to validate your thoughts either way?


  [1]: http://ux.stackexchange.com/