A picture says more than words: http://imageshack.us/photo/my-images/823/pycoders.png/

Edit: It seems to be caused by the sign up form. If I delete that in Firebug the content is centered correctly. This code seems to fix it:

    #mc_embed_signup {
      position: absolute;
    }
    
    #templateContainer {
      margin-top: 136px;
    }

Not a very nice solution but it works.