Wirelessly posted (BlackBerry8530/5.0.0.601 Profile/MIDP-2.1 Configuration/CLDC-1.1 VendorID/417)
I think that one gets relatively poor value by crediting car rentals to hotel programs, Amtrak, or most domestic airlines unless there is a significant bonus points/miles offer. I regularly credit both Hertz and Avis rentals to Virgin Atlantic, and invariably earn 1,000 miles per rental, even for one-day rentals. No surcharge, either.
Virgin Atlantic miles can be redeemed for travel on a number of airlines, including CO, HA, and US.