From a talk by Jeff Barr, Amazon's Web Services Evangelist:
Smugmug is one of the biggest customers for Amazon.com web services (meaning they could be invoiced if they wanted to be). However, they are billing everything on a American Express Platinum corporate credit card with the highest credit limit ($100K). Jeff says every month they probably earn three or four first-class tickets based on bonus points.
According to Jeff, their rate of growth is astonishing (Jeff said that they are
storing about 15TB (yes, Terabytes) a month in S3). What happens to images in Smugmug ceases operations? Well, apparently the family has committed to a multi-generational commitment.