But not as safe. There was news about people putting their own QR codes on rental bikes so that people mistakenly send cash to them in China.

It seems to me that QR codes could make it easy for someone to replace the original QR code with a different QR code at any place that accepts them and the merchant is none-the-wiser (unless there is some form of integration back to their PoS system) -- it seems like this could be a new form of skimming (stick your own QR code over any merchants :-)).

If most are screen based, you could just dynamically generate them and have them expire after N minutes. If someone wants a printed one make them jump through an application process for a long standing code.

They do for individual payments but storeowners sometimes tape their printed QR codes to walls and counters and they seem to want accommodate this use case too (essentially POS-less or "bring your own POS")

A great platform for what?

It's only as useful as the payment sourcs, and us credit/debit cards are terrible. I don't see how qr codes could do a lick of good.

I don't think it would be much of a stretch to get people used to them. The concept is already there with mobile boarding passes and some phone-displays-barcode loyalty apps like the one for Starbucks.