Turns out, IE misreads something in the way the CSS margin is handled, so it was putting the sidebar on top of the articles, and leaving a big sidebar sized empty space to the right. Microsoft's incompetence at simple things (implementing CSS) strikes again.
I tested it in BBEdit's internal HTML viewer, in Safari, and in Firefox (which rox, as noted in the sidebar). Each worked perfectly. I don't have IE installed because it does not rock. Not one bit. Like all Microsoftiana, it looks crappy, and works poorly.
Nonetheless, fully 42% of my recent readers use some sort of IE, so fix it I must. (If the bug only exists in IE 5, I'm only dealing with 5% of my readers, but I'd fix a bug that affected only one reader.)
Lesson for me: test with IE.
Lesson for my readers: If you don't already use Firefox, click that button up top and install it. Install all the adblocking goodies, and toss Greasemonkey in there to rewrite websites on the fly. Firefox is fast and it works right.