not sure if this is a targeted promotion or if it's for everyone, but i received this offer from thrifty:

offer good from 15aug00-15nov00. aviators members renting a thrifty car with a twa flight will earn double the normal 75 miles per day plus 750 bonus miles with a minimum 2-day rental (non-twa flight earns 50x2 per day + 750 bonus miles on minimum 2-day rental).