I contacted a local radio station (San Francisco Bay Area) and received the comments below from their Chief Engineer:
As far as "HD Radio" goes, we are not on with it now. We are scheduled to begin next year, probably in the summer. Our audio quality really won't be any better with it in my personal opinion. It will be heavily compressed and there will only be an improvement in the signal to noise ratio if the digital signal works well in your receiving location. As far as FM goes, the existing analog signal won't be degraded much, though some published studies indicate that the overall analog receivers signal to noise ratio is degraded, the "new digital" channel (or channels) is a very low bit rate of something like 96kb. The codec that the system uses, which is not upgradeable has some issues, though reports I have heard state that it's "quite listenable".
On FM channels that "multicast" (add more channels), it all is the divided up 96kb, so the overall quality degrades as you add more channels. I am not really sold on all of this at this point in time. We will see what the market thinks of it, and we will do the finest installation possible, to give the new system the best chance of success, our listeners deserve that.
Based on comments received so far, it sound like HD radio is not living up to the marketing hype. It may be too early to adopt this technology and I just hope that it gets better over time. I am no longer looking at HD radio.