in my mind, the options to overcome the excess whitespace are:
(A) Keep your content short, and use More… tags if it goes too far down the page. So every webpage is only 1000 pixels high or so. Or,
(B) Fill up the sidebars. Now obviously no one likes clutter in the sidebars. On the other hand the Body content is more comfortable to read when there is Something happening in the sidebar, instead of empty space.
(B-1) How about either, a darker fanicer graphic (like one of those curly-wallpaper backgrounds) that fills the sidebar but only the unused part, leaving the top part of the sidebar as-is.
(B-2) Or, how about a Plugin that calls as many Random photos or Flicker thumbnails as you need to fill up the sidebar, dynamically detecting the height? Just an idea, I would have no idea how to make that.
(B-3) Or, somehow make CSS that shifts your body content to be wider, or to be more centered, once it gets down to the area where the sidebar is empty. This seems difficult to code, if not impossible under current Standards.