In an argument elsenet, I've claimed (per Publication 526) that if you get a benefit from making a charitable donation, the value of the benefit has to be subtracted from the amount of the donation to get the deductible amount. That much is agreed.
I claim that it doesn't matter who provides the benefit. That is, if someone donates $500 to a charity using a credit card, and gets 500 airline miles as a result, the value of those miles (e.g. $5) must be subtracted from the amount donated to get the deduction. Others claim it needn't, that the full $500 is deductible.
Publication 526, in the rules, states that "If you receive a benefit as a result of making a contribution to a qualified organization, you can deduct only the amount of your contribution that is more than the value of the benefit you receive." However, all of their examples are cases where the benefit is provided by the contribution's recipient, not a third party.
I couldn't find the section of the Internal Revenue Code that specifies that only amounts in excess of value received are deductible.
Seth