Wireless barcode reader
If I ever get around to trying to catalogue my book, CD, dvd and (possibly) vinyl collections, a device like this would make it a breeze.
However, it's not too likely that I will (barring an enforced time of bedrest, and a willing assistant to carry said books and such), so I don't think I'm ever likely to get one…
Pity. Where I can see it getting a lot of use is in stock rooms and the like. Now, there, it would be handy.