I found very easy to register on Foursquare, especially when you already have a Facebook account. It was very nice to see all the options of places I can go, but the most interesting part for me was that I can go on my friends' profiles and I can check all the places they have checked in. Great tool to find out all the places your friends went and didn't invite you...lol....just kidding :)
For the QR Codes, I already knew how they work, so I didn't have any surprises. I downloaded the app and scanned QR Codes that I saw at the mall or on food packages. It is for sure a great tool to give extra information to people.