an interesting video with lots of sway info. They are demonstrating GM's Sway Stabilization Control, a system that detects trailer sway and apparently applies vehicle braking to dampen it.
Bob H lead me to the site with a different thread -- Thanks!
The first chunk of advice was to balance your trailer.
Folks who are contemplating putting a load on the rear of a trailer should take special note of what the GM testers do to the trailer to set it up for bad sway to test the system...