First, thanks for setting this up, guys - very exciting!
Second, here's a datapoint for you to work on:
SFO
National
6/23/10 11:00p - 6/29/10 3:00p
Fullsize
1) Default search gives me $503.36, which is the no-code rack rate.
2) Adding National contract 3715444 (Car & Driver) and coupon NF2853JDU (Entertainement 5-day free day) gives me $397.83, which is the Car & Driver rate, but without the coupon applied.
3) Entering both directly into Nationalcar.com gives me $336.53
Also, it is possible to enter multiple contracts and coupons for one rental car company? If I try to add another option line on the search page with another National contract/coupon, I get: "Discounts cannot be applied to the same company more than once."