Depends who you are. If you're MSFT, IBM, etc then you don't even send a no thanks letter, you have nobody who isn't a certified HR person talk to a candidate and you don't allow any off the cuff remarks. The lawyer target cross section is too high.

If you are a small startup in a high tech hub trying to attract people, and especially if you are in a market where the programers you reject might be future customers then you're risk is different.

Companies often forget that the people they reject don't disappear. It used to be a big thing in merchant banks in the last boom to really grind and humiliate candidates - you aren't smart enough to work here etc. What they forgot is that those people went to work for companies that might need a merchant bank and that the victim is suddenly the customer.