Barcr is an open source UPC barcode reader for Nokia Series 60 devices. Early Alpha at the moment, but worth watching. See also the ColorCode stuff.
We talked about real world barcode annotation a few months back but now the idea seems to be picking up steam. The Semacode system seems to offer an interesting take on the matter, but I’m betting that in the long term it will need a concerted commercial push from a major brand name before these kinds of barcode information services take off in a big way.