Having used a Squeezebox system for a couple of years, I decided to upgrade to what must be the 'gold standard' for wireless hi fi. The S5 is part of a wider Sonos system at my home (S5, bridges, zone players and the CR200).
Firstly the software interface for the PC is much more user-friendly than the Squeezebox (which is rather clunky in comparison), secondly it works almost immediately out of the box, thirdly it's very easy to use - finally it sounds great.
The S5 looks like a bigger version of the Bose docking station, quite a bit bigger. I think it sounds better too - the Sonos system features a graphic equalizer on the PC and handset, so you can shape the sound to suit. I have one or two massive sound files (50MB +) and they sound better than a CD, the S5 and Sonos system definitely appear to have an audio edge over anything else.
The handset (CR200) is very cool. Album art appears, radio is easy to set up... it just works! The handset/controller is worth buying - it's the main reason I switched to Sonos.
The only minor issue is that the range seems 'ok' rather than exceptional, however I've fixed this by putting another couple of bridge units around the house so nothing drops out. You can name individual zones and control them individually or link as many or as few as you like...
Cost is the only downside with the Sonos system, however I have to say that once you've used it, it is actually good value. It's well made, looks very 'Apple-like' and seems to have bullet proof software.