Piers,

well done you for having such a single minded approach. If that is what works for you, go for it.

Doesn't mean that's what works for everybody though, surely?

Plus, if I'm singing a song I've practiced at a folk club, however much I am concentrating on singing the song, I'm doing other stuff too - blocking out the noise from the bar, coping with the irritating tickly cough I've just developed out of nowhere, blatantly ignoring the rude b*****r who came in and slammed the door in the middle of my second verse and then sat uin the front row flicking through his floder of songs with one hand and checking his text messages with the other... so one of the things I need to practice, after I've done my initial learning of the song, is how to sing it while other stuff is demanding my attention. And so while my delivery whilst concentrating on driving is probably not live-performance-worthy and in itself probably doesn't do the song justice, it does do what Tom described in getting it into the automatic bit of my brain. (and when performing, even without irritating distractions of any kind, I still want to be concentrating on my communication with the audience, primarily, not a navel-gazing focus on getting the words & breathing right... so that still means I'm concentrating on several things at once)