While I remember seeing them on the BBC's 'Tomorrow's World' some time ago, I never realised that 2D barcodes were out in the wild. It appears that DoCoMo phones come with a piece of software that can use the camera to interpret these little squares of gibberish and return various bits of data.
Here's my URL encoded as a QR-Code (the standard used by DoCoMo so far as I can tell) created using this website.
Update: According to Mason Mouse, UPS have been using these things State-side for some time now; I guess it wasn't so exciting after all…
And if you cross your eyes and stare at it long enough, cute fuzzy bunnies appear! But I just saw them in my oatmeal too so maybe it's just me.