(MikeC isn't the only audiophile here)
Most definitely not! The forums are full of audio-interested lurkers. Roku SoundBridge
looks very interesting too, almost identical functionality?
Not quite. The Roku is basically intended to work in conjunction with either iTunes (which I can't comment on, as I don't use iTunes) or Windows Media Connect.
WMC is the server-side part of Microsoft's PlaysForSure technology suite. It's what they use to stream media to the Xbox 360 if you don't have a Media Center PC. The big advantage to PlaysForSure compliance for Roku is that they can play back DRMed WMA tracks. (Yes, DRMed stuff is generally stupid -- but the subscription music places are actually really sweet, and a good example of a business that doesn't work without DRM.)
That's the advantage of the Roku. The downside is that it sucks. The UI is incredibly clunky and awkward, compared to the smooth and elegant device UI on the Squeezebox. Browsing and playing music in the Roku is frustrating and slow, whereas the Squeezebox is natural and fast. The Squeezebox's UI is amazingly good, and you won't appreciate how good it is until you try the competition.
From an audiophile perspective, Roku isn't even trying. They revamped their model recently, and now they do a sample rate conversion on everything: If you send 44.1 KHz audio (which is what all CDs are), they resample it to 48KHz in the device. This affects the digital output, which means they can't even achieve bit-perfect digital output, never mind the analog output.
After owning a Squeezebox 1 for a while, I bought a Roku because I wanted to be able to play back my Yahoo Unlimited music. After a few days, I hated it so much that I returned it and bought a Squeezebox 2. Sure, it can't handle the DRMed music (although they recently added native support for WMA, and have hinted that the DRM stuff is in the works), but it handles my collection of WMA Lossless CDs flawlessly, and I love it.