The FCC adopted service rules for "white space" devices this year. The rules dropped the requirement that white space devices sense whether there is signal on a TV channel before they start transmitting, but the devices are required to access a database listing available channels for the type of device before going into transmit mode.
There are some experimental white space systems in place, but I haven't seen a rush to bring commercial and consumer white space devices to market. While the FCC has yet to certify database administrators I suspect another reason we haven't seen much interest in white space devices on unused TV channels is that there aren't that many unused channels where most people live.
I'm sure companies like Microsoft and Google are watching the FCC's plans to reallocate TV spectrum to wireless broadband companies. Broadcast spectrum is already tight in densely populated areas and if the FCC takes away broadcast channels in the top markets the few channels that are currently open will disappear. White space technology could be the answer to lack of broadband access in rural areas, if companies are willing to make the investment. Vacant VHF channels should work well for long-haul fixed links while UHF channels will work well for "last mile" connectivity to remote homes and farms.
If companies announce plans to roll out white space devices and services in 2011, perhaps the FCC will reconsider its plans to eliminate up to 20 of the existing TV channels across the nation.