Thanks Steve, you're right on the mark.
On my way in to work today, I stopped at the dealer to have a look at the various parts. While looking at the part of the intermediate shaft in the steering lock housing that couples with the switch, my first reaction was how spindly it looked. Sure enough, when I got to the car and removed the tumbler/steering lock/switch assembly, it was the spindly part that broke. There were several little crumbled up bits that fell out when I removed the switch.
In your experience, is there increased resistance to turning in the switch, over time, that puts extra load on the shaft turning it, or is it just inadequate engineering of the shaft itself? I'm wondering if I should replace the switch as well as long as I'm in there.
Also, do you know any way of strengthening or reinforcing the shaft to prevent it from happening again?
Thanks for your help