I should just close this out by noting that the offending ad was removed after the weekend. Our ad provider was quite apologetic, because we'd specifically rejected this ad unit already (not due to its size or placement, but rather because it re-expanded periodically after shrinking and it reloaded periodically even after being dismissed). Presumably the CPU load some of you reported was a separate issue entirely.
They've promised to take better care in the future, especially during weekends when there's no one around to put out fires.
Sorry for the problem, and thanks for your patience.
Stephen "Blue" Heaslip
Blue's News Publisher, Editor-in-Chief, El Presidente for Life