Hold your lense over the iPhone's camera. Notice that when you switch to your camera app, objects closer to the lens are much clearer. Using the snappr.net
app, you can actually scan barcodes effectively!
In the first set of pictures, without the lens, the barcode is blurry and will not work with snappr.net app. In the second set, with the lens applied, the barcode scans fine.
Note that even with the macro lens it takes some finagling to get the barcode to be recognized by the app. It's not perfect, but is really promising. Also, some books have huge barcodes and don't work so well with this lens.