Well, my 2003 Sierra 1500HD SLT was one of 3,912 optioned with Quadrasteer out of 39,006 (per CompNine). The truck is well-equipped (i.e. one of 3 trucks with all options), but it looks like the rarest feature was actually the color...Torreador Red Metallic (1,656).
I see a fair number of Denalis around the Dallas area. But I would bet that the Suburbans/Yukons with QS are every bit as rare as our trucks.