Really helpful, guys!

Blogger have decided to add a "clear:both;" explicitly styled <div> top and bottom of the post bodies. The effect was to drive the post bodies below the archive panel on the right hand side, which is pretty sub-optimal.

So I've had to wrap an extra <div> around it, and "display:none" all <div>s except those that explicitly override it. More non-semantic mark-up and weight on each page. *sigh*