It shouldn't be news to anyone at this point, but I've been asked about it a couple times lately so I'll post it here for everyone.
According to the FCC [pdf link], when the digital TV transition occurs on February 17, 2009, it will no longer be legal to use wireless microphones (as well as any other device that operates under Part 74) in what is commonly called the 700 MHz band (specifically, 698-806 MHz). Wireless microphone users may know this area as Sennheiser's C block or Lectrosonics' blocks 27, 28, and 29.
A lot of amateur filmmakers and even some small professional production outfits have seen these units at bargain prices on eBay lately and thought they were going to make out like bandits. And all will be well, until early next year...
Actually, I don't know exactly who won the auctions for the frequencies in question, or how quickly they will roll out products that use them. I wouldn't encourage anyone to test the FCC on how strictly they'll enforce this ruling. If the spectrum is used for a network similar to the current mobile phone network, it very well may be impossible to use these frequencies whether the new rule is enforced or not.