Drove from Bedford to Sandy listening to my internet radio* to see how well it performed (finally I can get JazzFM again!) and as long as I had a bar of 3G/HSDPA there was no buffering.
Unfortunatly about half way between the two towns the signal dropped out completely.
So while the clarity and choice is superior to DAB, it still needs a signal to work
Although in towns and along popular routes there's more likely to be no issues.
*web browser, sat nav, camera, emailer, remote desktop viewer, mp3 player, movie viewer, games console, oh and phone.