jonesy
Guru
I recently got an internet radio and it is fantastic, thousands of stations from all over the world (e.g. Bolivia Web Radio has great music), also can listen to 'listen again' stuff from BBC and also podcasts from anywhere. It can also stream music from my computer and play it through the built in speaker or plug it into the Hi-fi. Sound quality probably won't match good DAB but its still pretty good.
Actually the sound quality from internet radio should be better than DAB, as the bit rate is higher; for BBC channels certainly. Indeed, part of the controversy about DAB because broadcasters are using lower bit-rates than were originally intended, and the fact that the BBC is streaming at higher bit-rates via the internet than they are using on DAB rather suggests they think a higher bit-rate is necessary.
See:
http://www.digitalradiotech.co.uk
Of course, neither system will match FM with a good aerial and receiver.
Edit- I think one reason people report very high quality from DAB where they can get a decent signal is that many of the new DAB radios are very good, and very easy to use, irrespective of the limitations of DAB, so are an improvement on what they used previously. I've got a Sony DAB radio, which certainly isn't the best of the bunch, but neither was it very expensive, but it sounds excellent on FM!