In the fall of 2006, the AIA polled 2,448 of its own members (which is to say, professional architects), who got to name up to 20 of their favorite works of American architecture. Works receiving six or more mentions, of which there were 247, were then presented to a sampling of 1,804 U.S. adults in December 2006-January 2007. There's a little more to the methodology, of course, but that's the gist.
It looks like MAYBE I wasn't ALL THE WAY off my rocker in the "Is it possible?" thread, after all.
Cheers!
GFS