QR codes are EVERYWHERE in Korea. It's on just about every outdoor ad, in the subways, on buses, fliers, newspaper/magazine ads, often with colorful designs integrated into it. I went to a photography exhibit this week, and even the artist tag next to every photo had a QR code on it. Compared with launching your browser and typing in the URL, launching the QR scanner and snapping a picture is much easier.
I must admit, I think they're pretty popular in the UK now as well. Every time I go through the underground or flick through a newspaper/magazine I see them.