couldnt coinbase.com basically do that, your btc is denominated in usd anyway, so if they issue debit cards linked to your account then whatever the USD amount you charge will just be converted to btc and taken out of your account.... I think i will email coinbase..
i think this would be very cool and would make btc all the more useful to the average person. then again, i have no idea how that would really work in practice.