I know you have to rent cars frequently, but it might be worth it to some. Here is the promotion from National/NWA:

https://www.nwa.com/cgi-bin/promo...mo_new.pro

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# You must register with your WorldPerks number to qualify for this National Car Rental promotion.
# You must complete six (6) car rentals, for three (3) days or more per rental, of a mid-size or larger vehicle between December 10, 2007 and March 10, 2008 to earn 25,000 Wo...