SqueezeBox all the way
I've got the one of the original handbuilt sliMP3 players and one of the newer SqueezeBox3's, both streaming easily from my Netgear/Infrant NAS.
One of the biggest strengths of the SlimDevices/Logitech solution is the software, its very customizable (with gui's for all types of phones, and smaller screens) and it has a very active development. and it looks like Logitech has done exactly what it should have done with the purchase, uses its larger size for more 'fancy' models. The Duet and the new boombox version are good editions. Which you can add (and sync if required) to any existing setup.
Also for the proper audiophile there's the £1k Transporter which has excellent sound quaility (although there is also an active hardware modding scene for the 'normal' squeze boxes).
For someone that likes the idea of multiroom, but have different requirements/space in each room, i'd say the logitech solution is the most flexible.
The Sonos is impressive, but so far I've not seen any review saying it outclasses the squeezeboxes in audio quality, so why pay the extra money??