For those that don't have a 2D barcode reader for your phone, you can find one here. And for those who aren't yet up to speed on QR (Quick-Response) codes - they are essentially next-gen barcodes that serve as hardlinks/hyperlinks to some sort of content. You snap a photo of them and the software on your phone recognizes the data, sending you directly to the desired destination. It isn't yet a native feature on the iPhone, and you have to jailbreak your phone to install the iMatrix app to read them. This should be taken care of with iPhone 2.0 this summer. The are huge in Japan (developed by Japan's Denso-Wave in 1994) and now all over the place in the UK.
You can create your own QR code over at Kaywa, like I did for the seedwatcher blog: