What are the most adopted use cases for QR codes? Do alternatives or variations provide better user experience?

I know that QR codes are used a lot in some cultures (e.g. China and Japan) but are there any statistics on world wide and/or country specific usage? To be honest, I've never seen anybody use a QR code where I live.

Background: We're thinking about implementing QR codes on a classified website (customers can print their ads in newspapers, on handouts etc. - a widely used feature).

And of course: And are there any good alternatives to make the switch from print to mobile/web easier for the user? (printing URLs or "quick links" doesn't count ;-))

Update: Just found an interesting thread on Quora about QR codes adoption: http://www.quora.com/QR-Codes/Why-havent-QR-codes-become-more-widely-adopted-outside-Japan?q=QR

Update II: LukeW just published some stats on Mobile QR usage