Just some quick stats from what I've got so far:
Shows by network affiliation:
PBS - 12
NBC - 6
CBS - 4
ABC - 3
UPN - 1
States with more than one:
PA - 5
MI - 4
OH - 3
NY - 2
Size rankings of markets with shows (of the 210 Nielsen DMAs):
1*, 4*, 5*, 8, 9, 16, 22, 23, 25, 29, 32, 41, 42, 44, 60, 65, 66, 74*, 93, 98, 102, 108, 110, 113, 178, 180, 187
*Station does not appear to serve entire market
Most surprising stat: Only 2 shows west of the Mississippi.
Seems that the markets most amenable to HS quizzes have between 250,000 and 2 million TV households. Hm.