QR Codes Community
I compiled from as many sources as I could find, QRcode ideas for libraries at http://goo.gl/fb/HBJn
Its very long, so let me sumarise
There are many use cases but I think they can be classified among these 2 aspects.
(1) Embed QR codes in the virtual world (e.g. blogs, online catalogues, webpages,)
(2) Add QR codes in the real world (e.g. At book shelves, checkout machines, posters)
The other aspect seems to be what data is embedded in the QR codes, again there seems to be two main choices
(a) A URL (maybe even to a RSS feed)
(b) Some other data (Text, SMS, Phone number, email)
For (1) vs (2), I think (2) has far more potential.
It seems to me though, that the use cases for (1) , rests on the assumption that users are surfing on a regular desktop/laptop and then want some fast way to get information from the screen to their mobiles. Libraries are currently betting that mobile surfing will become huge in the future, so the importance of these use cases might diminish a little.
For (a), it also seems to presume that many of the library pages are mobile friendly so you can push the link there. You could of course push non-mobile friendly sites, but would be less seemless.. Thankfully most web2.0 services are mobile friendly, so you could add facebook fanpage, twitter , blogs etc.. Report shows use of social network sites is huge on mobile phones anyway!