The advantage of not having fees does not materialize for the client, so he's unlikely to care that the shop is saving money. The customer drives the demand for a payment method - the shops are forced to follow or loose market share. The shops would get rid of credit cards in a hart beat if they could get the customers to pay with cash.
If a merchant can save X% by accepting Bitcoin instead of Visa (due to combined CC fees plus chargeback fraud), then one might imagine merchants will lower their prices by X-Y% to anyone paying in Bitcoin. Thus, the savings for the merchant will start being split between the merchant and the customer. A customer may get to pay 1-2% less for products when using Bitcoin.
So aside of the phony geek appeal, what does this system offer to the customer ? Credit cards offer interest free loans for up to 2 months, emergency funding past that period, and money back guarantee. Bitcoin offers final indisputable transactions - why do you think customers will prefer it ? Status Quo:
A world where every time you shop with a vendor, you expose your financial and identity information. You must trust their systems, staff, and intentions. Sony customers have been enjoying this risk. In 2009 there were over 10 million US adults who were victims of identity theft... Bitcoin Alternative:
A world where every time you shop, exactly zero of your financial and identity information is exposed. Vendor doesn't even need to know your name, let alone address, CC number, etc.
I prefer the Bitcoin Alternative to the Status Quo. Why don't you?
Don't even get me started on the clunky desktop client that kills your harddrive.
Few people will use desktop clients for day-to-day Bitcoin use. Ewallet and online banks will serve that purpose on a PC and mobile apps serve the purpose on handheld devices.