To requalify for CO Silver (more a hobby than a necessity), I recently booked the following from my semi-home airport, ATL:

FLIGHT INFORMATION
Day, Date Flight Class Departure City and Time Arrival City and Time Aircraft Meal
Tue, 23OCT07 1621 X
ATLANTA(ATL) 7:00AM
HOUSTON BUSH INTL
(IAH) 8:09AM 737-500 Snack

Tue, 23OCT07 441 X
HOUSTON BUSH INTL (IAH) 9:55AM
AUSTIN TX (AUS) 10:54AM 737-500

Tue, 23OCT07 1758 L
AUSTIN TX (AUS) 12:40PM
HOUSTON BUSH INTL (IAH) 1:39PM 737-500

Tue, 23OCT07 1015 L
HOUSTON BUSH INTL (IAH) 2:40PM
DALLAS/DFW (DFW) 4:00PM 737-300

Tue, 23OCT07 1570 L
DALLAS/DFW (DFW) 4:40PM
HOUSTON BUSH INTL (IAH) 5:50PM 737-300

Tue, 23OCT07 1720 L
HOUSTON BUSH INTL (IAH) 7:25PM
ATLANTA (ATL) 10:47PM 737-500

This cost $253.90 all-in. The cpm is not great, but it's the chepeast way I could find to requalify out of ATL in a single day. By the way, after using Dream Maps to find the low fares, I searched co.com for ATL-AUS, AUS-DFW, and DFW-ATL.

Has anybody else transited an airport (in my case, IAH) three times in a single day?