I think the "clearfix" class should be added to the "Body" div, in the "menu.php" theme file:

[ln 27] echo '<div id="Body" class="clearfix">';

The "clearfix" class (which is already in the default "vanilla.css" file) is a hack designed to fix an issue where a floating element flows beyond its container box/div. If you want to place a margin on the bottom of "Body" div, you get an issue where the Panel flows beyond the bottom of the "Body" div. This happens on pages where the Panel contains more content than the "Content" div. This is most obvious on the Account page.

Unless there's some issue with the "clearfix" hack I'm unaware of, I think it should be added to the core "menu.php" theme file, to save Style designers some trouble.