Who Uses Mag 2-D Barcodes?

In ADAge: Key findings " ...  Among Readers Who Saw Ads with Codes, 4% Snapped a Picture, Gfk MRI Starch Research Says : As quickly as interactive 2-D barcodes and symbols have spread through magazines -- check out Glamour's September issue, where you can scan Social SnapTags to "like" an advertiser on Facebook and get special offers -- it's been hard to tell how many readers actually use the things ... "