Congratulations, Colin. Your pricing model has people thinking about your service in terms of "a markup over Amazon S3". =)
A critical part of trust is transparency, and in the long term I think I'll do better by having transparent and obviously reasonable pricing than by obscuring things and trying to maximize my (short-term) profits.
I didn't know about either of your companies but by the discussion, its clearly possible for Tarsnap users to derive value from the trust associated with transparency and feeling like their dollar is maximized. tptacek, pricing schemes aren't the only component of the purchase decision or profitability. His users are making a more emotional decision. cperciva should stick to the core of what his users are finding valuable...then get bought out and turn into an evil profit maximizing company
Using S3 would cost me more per month unless I implemented a similar system to tarsnap.