However, what is noticeably missing from their marketing materials is any acknowledgement larger than 6pt type that NONE of these satellite radio receivers work in North America without a clear line of sight view of the southern sky. That's right. Your new "portable" XM radio won't work inside a building. GPS has the same issue as do pretty much all satellite-based consumer products.
Satellite TV works because the dish can be mounted permanently to the roof of your house. Satellite radio in cars works because most roads give you enough view of the sky to work and GPS's similarly. However, given the expectations of what a "portable music player" should be that MP3 players like the iPod have given consumers, most people who buy one of these XM setups are going to be disappointed.
The net result of this is that XM and other satellite radio services potential market is limited to those traveling in the open (i.e. cars where you can have the receiver look through the windshield) and those who are stationary (home stereo setup along with your satellite TV). Those aren't insignificant markets to be sure. However, clearly these companies saw those as inadequate to sustain their business models or you wouldn't see the portables coming out.
And, with the rise of podcasting that gives people a huge variety of content to use portably and asynchronously (I'm listening to a hilarious presentation from PopTech right now), that's FREE instead of $10/month, the competition is going to be fierce. Not to mention the various unlimited song services with portable players that give you playlists 1 million songs long whenever you want them.
All I can say is "Good luck, XM." You're going to need it.