The "professional courtesy" rate gets used quite alot in my office. Anyone in the dental field will atmost(and even then not very often) see a materials only charge(i.e. lab bills for crown and bridge and the cost of the bleaching kit), and alot of the local medical docs will have the same coutesy extended to them (we do charge ER docs(generally 50-75% of the regular fee) since they can't make bills "disapear" like M.D.'s in other fields can. Hey, I even extend it to my 2 dogs vet(he had a root canal and a crown done for the crown lab fee only last year and one of my dogs had to be declawed(very weird autoimmune disease against her nail beds) and all I saw a bill for was anesthesia and pain meds last year. It's the old, you scratch my back and I'll scratch yours principle. Plus it goes without saying that if I feel absolutely miserable and want to go see my primary care Doc, that one phone call and I'm seen within and hour or 2 and I won't see a bill for anuthing more than lab fees, and vise versa if he, or any of his family has a tooth problem, they're in my schedule ASAP. In my practice, we have that type of arrangement with internists, primary care docs, general surgeons, opthamologists, OB/GYN's, Pediatricians, a Pulmonologist, a GI Doc, and a Urologist. Plus with the network they have, any other doc we need access to is just a qucik phone call away, and they know they have the same situation when they're in out office.
My partner and I have our first soon to be a dental student (likely class of 2008) in the practice now and if she wants us to do any work while she'sn school, it will be on the house. Although, I will admit that there is a litle bit of classmate bonding that does occur when you get to learn how to do a cleaning on your classmates that I reccommend that nobody miss out on.