Before I tried out the Sonos system, I'd been satisfied with my Airport Express setup. But no longer. The Sonos system has raised the bar. Even though there were some rough spots, the positives for Sonos far outweighed the negatives. Of course, given the price of the system, that had better be the case.
The major drawback is DRM. Most of my music library is composed of mp3 rips from my own CD collection, but over the last couple of years I've been slowly accumulating music from the iTunes store. The fact that these songs are not playable on the ZP80 is no fault of Sonos, though. Up to this point, Apple has refused to license their FairPlay DRM system. Nothing but Apple products can play back music purchased from the iTunes store.
The DRM issue is not unique to Apple, either. As I pointed out above, neither the ZP80 nor the ZP100 can play Microsoft "Plays-For-Sure" DRM-encrypted content, either.
But this still has to be a concern for Sonos since there are many people out there in the same boat as me. Apple has sold over a billion songs in the last few years and none of them are playable on the Sonos system. But you'll have to judge for yourself whether this is a concern. If you don't need to play these DRM encoded files and you're willing to pay the price for this expensive system, you will find an elegant, well-thought-out system that is a pleasure to use.