Pros: Low cost compared to other solutions, nice design, works, great feature set.
Cons: Shuffle is unsophisticated.
The bottom line: The Sonos is everything that it is advertised to be.
My wife and I live in a 3 story, 3000 square foot house. We love music, and wanted music available for when we entertain. We considered in-wall wiring and mounting of speakers, but that was disfavored because (1) it's expensive, (2) it's intrusive, (3) you can't take it with you. That project would have cost over $5,000, and involved contractors and whatnot tearing up the walls.

Then Sonos came out just in time. Place a Zoneplayer in each room, connect it to speakers, and you're ready to go. You control what each Zoneplayer plays via the Controller. Each Zoneplayer is a router, wireless access point, amplifier, and media player. Each Controller exists on the network as well. Sonos uses a mesh network, meaning it uses a proprietary network that exists on (I think) the 2.4ghz band. The Sonos system connects to your existing computer network via TCPIP. That's how it gets music and reaches the internet for internet radio stations. I have mine pulling music from a network access storage (NAS) hard drive. That hard drive is directly connected by wire to one Sonos Zoneplayer. That same Zoneplayer is also connected by wire to the incoming internet connection. From there, the first Zoneplayer connects to the others via wireless.

So, the Sonos does a great job of playing digital and line-in music, as well as managing your library. Other neat features include up to 32 Zone Players in a network, the Zone Players can be playing independently, or as groups of any size, each Zone Player is also a hub for your main network in case you need more RJ-45 drops, playing internet radio stations, compatibility with a wide array of formats including MP3, Ogg, WAV, WMA (I think). It does not play DRM music, but neither should you. You can also make custom play lists.

The only deficiencies are that it takes multiple menu steps to change internet radio stations, and that the shuffle algorithm isn't great. When you shuffle a given list of songs, it will play them in the same shuffled order every time.

Note that this is for playing digital music over primarily wireless connections. That means that for audiophiles who like gold cabling and have ears like bats, they will never be satisfied. But, if you're not quite an A/V snob, then you'll be impressed.