Hi Huw,
I've had a Napster account for a few weeks and it seems to work fine for me. They have a trial period so if you find the quality or service is not what you need you can always cancel before the trial expires

I would describe the quality as ok but only listened so far via MS200 and existing passive setup - the DSP's are still in the warehouse waiting for revovation work to be completed...grrr
My Internet connection is also pretty good ( virgin media cable 100mb) so that might help I guess.
I have spent very little time with the radio and other channels so these might be worse (or better ! ) I can't really comment.
Hope it works out ok for you
Regards
Phil