"Transaction issuers must pay for all rewards up-front" Will there be a way to make ongoing payments for data retention? With a proper API this could be used for secure distributed backup, that would be a killer use and something I would gladly pay "miners" for.

The way I understand it, Get'ing the data also publishes it to existing miners, so they can start storing it if it's a piece with a high reward value. The TTL is decreased by the Get operation, though. By understanding how valuable your data is you can choose a time to Put it again (while reward/TTL > market rate) with a new reward attached. Obviously that reward/TTL should be higher than the last one to buy you a bunch of safe Gets again.