there is a mobile app called keyring which you can put all your loyalty/discount cards into. i would think though that you would still not be allowed to use this for your target tm discount since the rules are that your cashier has to scan your paper card. waaaaay easy to let everyone scan your barcode and use your discount. on a semi-related note; targets mobile app used to have a barcode scanner in it which was pretty amazing except for the fact that it wouldn't give you a realtime price in your store - it looked it up online. not sure if it still works or not.
as far as scanning mobile coupons - it always seems to be a pain. if you have new scanners (they'll have a larger scanner surface area, as opposed to the older "slimmer" looking hand scanners -laser) they should work better, older ones still take a couple tried to get it to go through. and then on top of that it all depends on glare, if their screen is scratched, etc.
http://www.clresearch.com/research/detail.cfm?guid=65A9C4B6-3048-79ED-9994-223F43CFC435
also semi-related; i wish i could take the coupons i want from target.com, and just have them sent to my phone - like log into the app and get them that way instead of having to print them out, then cut them out, and waste all that paper and ink. but i digress......
oh and pps; does anyone use shopkick? are TMs allowed? haven't even heard anything about it other than seeing it installed, and the table talkers.