While there is a lot of hype (deservedly so) out in the marketplace right now surrounding QR code it is not the only 2D barcode symbology available on the market. In other words, not all 2D barcodes are QR codes. There are a variety of others, but I would like to direct some attention to one in particular - DataMatrix.
Like QR codes, DataMatrix codes can hold large amounts of data. DataMatrix codes, however, are especially suited for making very small codes and lend themselves to tracking and identifiying small items. DataMatrix codes are also thought to be more secure than QR codes and this combined with the redundancy of the code - which basically means the code is still readable even if up to 60% of the image is destroyed - is the reason the Department of Defense chose DataMatrix as the symbology for their UID (Unique Item Identification) mandate. The image displayed here shows a DataMatrix code used on a UID tag.
Don't get me wrong - QR codes are great and we're uncovering more and more applications for them, but there are other options available out there when it comes to 2D barcodes and it just comes down to a matter of what you are looking for and what you plan to accomplish with the barcode, i.e. what are you tracking/identifying.