I've used QR codes regularly enough in Ireland for loyalty cards on my mobile.
They work pretty well and I just "paid" for a coffee with one a bit earlier this morning.
One thing I'm noticing here is various attempts to use smartphone loyalty systems being hampered by laser scanner that can't read screen displayed barcodes or QR codes.
I've basically given up on Stocard because it rarely works or cause delays as they end up having to type it in manually.
Ultimately, business adopts technologies where they provide a clear advantage. In a world of ubiquitous contactless credit and debit cards, it's hard to convince people mobile payments are any great advantage.