Mashable has this graphic which is astonishing.  I hope some future information will report on the costs that can be associated with these gifts but whatever they are, I suspect they are small relative to the receipts.

Pay particular attention to:

1.  The average gift (much higher than I would have guessed).

2.  The age groups of the donors.

http://mashable.com/2010/09/18/social-good-infographic/?utm_source=feedburner&utm_medium=email&utm_campaign=Feed%3A+Mashable+%28Mashable%29