Bridging digital and real worlds
Not many technologies have managed to bridge the digital gap, like barcodes have. There is a couple of projects that aim to extend this type of real world / digital world binding and interaction, beyond warehouse management. The ones below seem to have potential, as they try to empower the user and not just deliver more ads...
I mentioned digitally signed ID cards with a barcode in an earlier post. Dataglyphs are a PARC Research's solution to embed barcodes within images themselves. And the Sem@code project build barcodes that encode urls and are readable using a cellphone's camera, which seems to overcome one of the main reasons the CueCat failed (it needed a computer and a wired device).
Some "bridging" technologies, like RFIDs, use radio frequencies to link the item and the device. nTag and SpotMe are devices that use wireless technologies to enrich some social scenarios, like conferences. I'd be curious to read some users' feedback on these.
There is also a bunch of location-aware products that are emerging (mostly phone based), but it is also hard to tell how useful they really could be, without seeing them in action.
Update: Slashdot has a story on nTags.
Update: Another cool use of barcodes with cellphones: the cellphone analyses the position of a circular barcode on a screen and transmits that information via bluetooth, to provide a new form of input mechanism. Slashdot's "Cellphone as Virtual Mouse, Keyboard" and the research page on these SpotCodes (with videos).
Update (2005/12/28): Semapedia is a Semacode to Wikipedia linking solution. It provides both label printing so that you can tag physical objects and a reader software for mobile phones.