Gyft has an app that not only keeps track of your GCs (not just Disney ones), but it creates a bar code for the GC on your phone. You can just use it from the phone with no need to carry your cards around with you. I plan to try it when I'm in Disney next time because I'd rather not have to carry a stack of GCs with me to Orlando on future trips.I'll still bring the physical GCs on my next trip but if this works, I'll leave them safely at home the next time. If I could just have the CMs scan the barcode on my phone when I make a purchase, then that's one less thing to worry about!
ETA: The Google Wallet app can also be used to add your GCs to one place. As with the Gyft app, a barcode is generated for the GC and the balance is updated. In Google Wallet, you can also take a picture of the front and back of the GC and store it in the app.