Tell me about "HD Radio"

I’ve been hearing a lot of ads on the radio lately for “HD Radio.” The main selling point is “listen to all the stations between the stations.”

Who or what runs and programs all these other stations? Are they sub-channels of existing stations, or new startups looking to make a success?

Obviously, these “stations between the stations” don’t have a lot of market share, since very few people have the new HD radios. How do they pay for programming, talent, etc.?

Are there HD stations out there with actual DJs, news, etc, or do they just program a computer to keep playing music 24/7?

Not too many stations yet. Only one in Knoxville and not interested enough to lay out >$200 for a radio of any kind.
All You want to Know About HD Radio