no i wasnt clear on that bit, i meant more or less having a bank that oversees the process , imagine going to a "bank" and essentially depositing bitcoin in return for "notes" that are sealed in pre determined denominations that you can trade with. until someone comes out with an instant transaction process for bitcoin i believe that is essentially the quickest method of transacting in store.
The bank is a centralized point of failure that may draw attack. If nothing else, the system that you describe would seem to have the moral hazard of the bank (either openly or by stealth) starting to maximize profits by engaging in fractional reserve banking. I think most in the bitcoin community would agree that fractional reserve banking is A Bad Thing.