Microsoft evangelist Robert Scoble has a post up of why you should buy anything else other than an Apple iPod(tm). You can read the article but, to me, it boils down to his saying, paraphrasing here, use our (i.e., Microsoft's) DRM rather than Apple's.
While I think he makes a good case about how you can find more MS compliant players out there, as compared to Apple, I say why use either of their proprietary, crippled software? Why lock yourself into a DRM jail that keeps you from using music you PAID for?
Why not use Ogg Vorbis or the almost universally accepted MP3? If you had music in these formats you could probably listen to them on even more players than either of the proprietary formats of Apple and MS combined.
However, as noted in an earlier post, you can convert from Apple's proprietary DRM format by burning an audio CD. This process creates CDA tracks which can then be ripped by your favorite software into whichever format you like and therefore playable on whatever you like. I don't know if you can do something similar with Microsoft's offering. If you you can, drop me a line using the email link over on the right column.
But the bottom line is, in my opinion, it is a false choice to say pick Microsoft's DRM over Apples' because you can find more players compliant with MS when you can find even more that are compliant with MP3. YMMV. Insert disclaimer here.
Aloha!