RickG:
I have a little bit of experience and information about both Sirius Satellite Radio and XM Satellite Radio. Right now, both private ventures are losing money but they sure as heck had a great holiday season in 2003! Sales of satellite tuners for homes, cars, and boomboxes for both companies really took off; I was a bit shocked with their sales numbers for this past holiday season alone. So, they are making more profits but they have yet to hit the black on their accounting books. That may take another year and double their current subscribers. Right now, Sirius has got between 220,000 - 250,000 subscribers while XM has 1.3 - 1.35 million. Those are not precise numbers.
In terms of features, XM has really made a number of strides to not only achieve parity with its chief competitor but with the traditional AM/FM broadcasters as well. For example, they got rid of all commericals for their 60 music channels just like Sirius. However, it should be noted that there have been a lot of complaints against Sirius for their "wooden" approach to their so called music streams: it's like a computer picks the same songs over and over again with very little human interaction. XM is a bit different in that they have live DJs at all hours of the day / night working to answer calls, play requested songs, introduce new artists / bands, etc. just like traditional AM/FM -- but without the commericals starting next month. Also, XM is going to innovate this niche market by adding 5.1 channel surround sound and video later next year. Not only that, XM has been granted permission by the FCC to carry local news / weather reports in major US cities with more major cities upcoming too.
Stereophile and USA Today now report that both Sirius and XM are well on their way to becoming a permanent fixture in the American radio markets with increased subscribers and innovating products not to mention stronger and stronger sales. Kind of makes me sad that I dumped mine but I wasn't using it too much.
So, what's the sound quality like on XM? It varies but in general it sounds like compressed digital music at low bitrates. However, the programming is top notch and it certainly is a variety freak's dream come true.
I think that the ultimate radio (which will never be made) would incorporate these features:
AM / FM
XM or Sirius (or both)
iBiquity HD Digital radio
Compact Disc
That's gonna be the killer radio but nobody has plans on developing it. HD digital radio is coming...soon. Basically, it's like AM / FM but with near CD sound quality, no noise / static, and the ability for marketers to push even more crap down your throat using both sound and videos. It kind of works like the Delphi SKYFi tuner in that you can see the artist & song + station at any time while downloading weather & news information too. You'll need a special HD radio tuner which is gonna be made this year. Good thing is that you don't pay a subscription fee. Bad thing is it will be pretty much like AM / FM but with multimedia content and tons of marketing. Good thing is your favorite AM / FM stations can still keep their names (and jobs) but you'll hear increased sound quality, get increased range, and less noise / static. Bad thing is that they will have to purchase iBiquity equipment to broadcast in HD radio which means that not all your favorite stations will get on the ball at the same time.
I hope this helps. My money is still going toward my reference rig.