I have a hard enough time picking up digital OTA signals where I live. All the broadcasts for the entire DFW metroplex are generated over 40 miles away on the south side, and I'm way on the north side. I had to buy a 10' directional antenna and an amplifier to get it work decently.
Back on topic, you'll definitely need a digital receiver when the time comes if you don't already have a TV that can handle the digital signal (such as my TV). That's really only going to be an issue for those people that don't use satellite, cable, or an NTSC receiver, and I'm pretty sure that number is shrinking.
Interestingly enough, a very large number of brand new HDTV's don't come with digital tuners built-in. They expect you to use a cable box, CableCard, external receiver, or sat receiver. It's just expected that if you buy an HDTV that you're probably also prepared to pony up the dough for premium content. As such, a lot of TV's just don't even bother including the digital tuner.
Digital tuners are getting built into nearly every new DVR these days (including lot of those used by satellite and cable companies). I've got my DirecTV HD Tivo and I'm ready for the revolution. I know that digital isn't necesarily the same as HD, but I'm hoping the push towards digital will help the push towards HD across the board. I've like to see every show on every network in HD.
Right now, it seems the only cost-effective way to actually get HD programming is through OTA digital signals. After you have a receiver, it's just free. Cable and satellite companies charge an arm and a leg for HD, and you usually get less than 10 channels to show for it. And if you want movie channels like HBO in HD, you usually take the double hit. You have to pay for the movie channel and the HD.