I would never rely on a qr code, we use unique qr codes in the hope we can track which of our advertising is successful and we use them quite extensively (we have one on our van (it's big!), one on our business cards, one on our flyers and one on our clothing labels) over the last year they have in total resulted to about 5 website visits.
also if your handing out a business card to a customer, don't underestimate the power of a phone number, a lot of our custom work comes from a phone call (then I request they email over pictures so you probably want to put that on there too) even though I've got a perfectly good, select product, click upload, pay your money interface on my website.