Jon and I looked at the Squeezebox, along with the Roku Soundbridge when we were doing R&D on our amp.
Both seem to have a very good reputation for sound quality. They both have excellent DACs and I think it is fair that they are calling themselves 'audiophile' products. You might meet snobbery of the "how can it POSSIBLY sound as good as my £3,000 CD player?" type but these are people for whom the actual sound of something is much less important than how they believe it sounds.
It looks as though "The Transporter" has an even higher quality DAC and is likely to sound even better to those with the ears to be able to tell the difference (i.e. not me). In fact it looks as if a lot of thought has gone into it. Very sexy.
If I didn't have a very similiar setup here already (Mac or Windows pcs via USB to a stupidly high quality DAC) I would have bought a Squeezebox by now.
I'd buy that over the Soundbridge partly because I prefer the idea of the open source client.