interesting concept. a bank of sorts. i wish you the best of luck in this complex business.
I'm not storing any balances or handling any funds - I am printing randomly generated numbers on paper, mailing them out, and forgetting about them, promising not to keep a copy. Once I send out a sheet, it's completely out of my hands.
We're to trust you not to keep them? Nope, not going to happen. No one in their right mind would trust an unknown 3rd party with full access. No offense, but this seems like a clear money-grab since the keys are a one-time use. Furthermore, this concept is not simple-for-grandma. A grandma isn't going to know what a private key is, how to use BlockExplorer, or know how to spend the money.
Or the modified bitcoin client.
Just seems like a half baked idea stolen from bitbills.