Colin,
Given the recent controversy around storing data within reach of the NSA -- did you ever consider hosting Tarsnap outside the U.S somehow?
Would it be impossibly hard to host the service on something else than AWS?
I know, the encryption protects the data, but it appears that the mere act of encrypting data actually increases the likelihood of the data being extracted by the NSA.
Regards,
Asgeir S. Nilsen