Video of it in use:
http://www.youtube.com/watch?v=eOman2F9G1M
I picked up a JVC KDHDR20 MP3-CD-HD head unit at Crutchfield for $99. That included a Saab wire harness worth $20. At Best Buy, they wanted $119 plus tax and had no harnesses in stock for my 900, nor did they carry them.
I hate how modern head units look like laser light shows for toddlers. Fortunately, this one just has a few tastefully colored red buttons, a knob, and a clean one-color readout with sharp text and good lighting. Nothing dances around. The dimmer, unfortunately, is manual, but at the lowest setting its viewable even with the top down.
Here's how it looks in the full dark.
This guy came along.
This is, of course, the remote. Due to a lack of preset buttons on the head unit, you have to hit Menu, then rotate the knob, then push the knob to select a preset station. With the remote, you can hit the up and down buttons to quickly scroll through presets. I fixed it to the top of the steering wheel hub with double-sided mounting tape for easy access while driving.
With HD, each major radio station has two or three digital substations. Some use them for deeper commercial-free formats, some duplicate their content, and some broadcast different formats entirely.
Example: 97.1 FM Talk has an HD2 adult contemporary/jazz station. 103.3 is an oldies station that uses HD2 for its traditional Solid Gold format that ranges from 1950 to 1965. 106.5 is like "Jack FM", playing all music from all eras, and uses its HD2 for more obscure songs. Some don't have substations.
Basically, my content has tripled. The tuner is very sensitive, rivaling some Delco radios from the 80s and 90s, so in addition to new HD content, I'm picking up stations I never knew existed. Unfortunately, 18 FM presets isn't enough for all of them.
The format is specific to the US, although various other digital audio broadcast formats exist in the world.
I was a huge proponent of XM since getting started with it in 2003, but like all good things, customer service dramatically worsened, prices increased, commercials were added, and audio quality on music channels was reduced, giving the bandwidth to expensive sports and talk contracts.
BONUS: HD radio sounds MUCH better than satellite. Once the tuner locks down the digital feed (it begins receiving in analog, then HD kicks in a few seconds later) the audio quality dramatically improves. Stereo separation widens, treble and bass move further out on the sound spectrum, and noise and hissing are eliminated.
BONUS 2: Somehow, it ended up using the EXACT same harness connector as the late 90s Blaukpunkt CD head unit I pulled out. All the wires matched up perfectly, so now I have an extra Saab wire harness. It even slid perfectly into the existing slot.
The only negative is that some of the smaller stations don't delay their digital feed. This causes the audio to "skip" or repeat for a second while it switches to and from digital mode. This tends to happen with stations that are far away or when sitting under a bridge in traffic.
For no cost other than the tuner, HD makes a stale format more competitive.