My question arises from experience a number of years ago with a food recovery program which based our pleas for donations on the Good Samaritan law (limiting liability for donors). To my knowledge, there had never been a successful challenge to this but that was quite some time ago. I have been away from our local "Waste Not" charity in the interim and do not have up-to-date information. Another post regarding how restaurants treat leftover piqued my interest.
When I was active, we had the most success with donations from small restaurants not most of the deep-pocket chains - Long John Silver's being the exception. These donated food programs, in cities around the country, make a significant difference in the operating budgets and program availability for the different charities by freeing funds otherwise needed for food.