Rather to my surprise, I have never received such a request. I don't know if this is because Tarsnap users aren't of interest to the relevant agencies, because

Rather to my surprise, I have never received such a request. I don't know if this is because Tarsnap users aren't of interest to the relevant agencies, because they know they wouldn't get anything useful, or because I'm in Canada -- I wouldn't be surprised if US agencies preferred to request data directly from Amazon rather than making a request to someone outside of their jurisdiction.