Well I guess ParkSFO has finally worked out the difference between business travel and personal travel! Rather than only being able to use coupons for a specific stay, you can now bank the free days for future stays. ie, make your expense account pay full price, and use the free days for your own personal travel.

There doesn't appear to be anything about it on their website, but the email is at Untitled Document

It'll be interesting to see how tax is implemented on the free days. They had some screwy rules back when they used to do the free day coupons without a minimum stay, but I forget exactly what they were as I haven't seen one of those coupons for close to 10 years...