The free rental days can be used between September 10 and June 16, 2013 on full size category or lower cars, with no more than 3 free rental certificates on a single rental.
You can earn up to 10 free rental days under the promotion, and registration is required.
Update: I misread the terms and conditions last evening, there is no limit to the number of free rental days you can earn. There’s an additional way to earn free rentals which is by referring people to the promotion, and they cap that offer at 10 free rental days. Note that my links to the offer in this post are not referral links, I am not asking you to register through my link, the links I’ve posted here do not provide me with free rentals.