Many people, including myself, are just starting to realize the potential of mobile barcode scanners. I'm not talking about using a mobile phone to generate barcodes for things like food orders (see this prototype of a Starbucks ordering system on the iPhone; thanks Tony for showing me this), although that mode of operation will also be revolutionary. I'm talking about using a mobile phone to scan barcodes on all kinds of objects in the physical world which provide a sort of hyperlink to more information about those objects, which is then displayed on the phone. Here are some examples to show how interesting this could be...
You could easily keep a written history of personal objects. You might find an old baseball bat in the attic, scan it, and read old entries, like, "May 5, 2012: Got this new bat for my birthday." Or, "July 12, 2015: This bat hit a winning homerun against the Tigers." You wouldn't have to keep a physical file cabinet full of records like this... they would be attached to the object itself.
The same principle would apply to public property. Imagine tying internet forums to specific places or objects. Forums usually assume a shared interest of some sort; in this case the thing you share is that you have experienced the same location or object. Sort of like bathroom stall graffiti, but everywhere... and hopefully more useful. Imagine walking through a park and sitting on a park bench. Embedded in the bench beneath a piece of glass is an inconspicuous little barcode. You scan it with your phone, which provides you with a few paragraphs about the park, the donor of the bench itself, etc.; sort of a Wikipedia entry. There are random text entries people have written, like, "August 21, 2010: It was rainy today, but I went for a walk anyway. Sat here for a half hour until it cleared up. Oh, be sure to smell the freesias about 30 ft NW of here," or, "November 7, 2011: I started reading A Brave New World here today. Has anyone read it? If not, check out the link. Man, Huxley was way ahead of his time." It also includes pictures people have taken nearby and "added" to the bench. And videos. Maybe even music recordings from the bandshell across the park. Each of these bits of info are tagged with dates, so the bench's entire history could be displayed as a timeline of local events. There might be problems, like people spamming the digital timelines of public property with advertisements. But we wouldn't have to hire people as spam filters to clean them up physically; all the data would be stored in the cloud, so there would be automatic spam filters.
Products you buy would no longer need paper instructions for assembly and usage. (Instead, you would get hyperlinked text, audio, and video instructions.) Nor would they need paper warranty statements. Even purchase information from paper receipts could be stored with a product's digital identity. When you buy a book, the store scans the book, gets your bank account info (by scanning your mobile barcode-producing device?), debits your account for the purchase, and transfers ownership from Barnes & Noble to you. Later, returning defective products is dead simple. Or, if you want to give the book to a friend, you perform a similar ritual to transfer ownership. So the object's digital identity could store the original purchase price, the current owner, and even the history of owners.
All kinds of physical objects could benefit from metadata. Easily keep car maintenance history with the car itself. Store your personal medical records on a bracelet. Stickers on produce would direct you to the harvest date, expected expiration date, the grower's location, and helpful recipes. Medication could provide personalized audio messages from your doctor and up-to-date warnings and recall notices. Musical instruments could hold audio recordings from previous owners. Paintings could link to more art from the artist. Power tools could give you tips on how to use them. The list of potential applications is really long.
Note that all of these things could be done without the barcode (e.g., keeping online documents which you can find via text search), but the barcode provides a context-relevant link to that data. Context is the key idea here: you can easily access the relevant info when and where it is needed. Replace (or augment) the searchable online file cabinet with hyperlinks directly from the physical objects.
Of course, other technologies could provide similar capabilities, but they're too expensive to be practical. Barcode systems are essentially available now, and they're so cheap, both in terms of the scanners (i.e. camera phones) and the individual barcode labels. They fit so easily into our existing infrastructure. You could print your own barcode labels at home and stick 'em on anything. Practically, all we need is a standard barcode format, barcode scanning software on our mobile phones, and free web hosting for all the metadata. Eventually such a system could evolve to include RFID tags, GPS devices, augmented reality displays, and Google Maps/Earth/Metaverse, but cheap barcodes could start laying the groundwork today.