Yo,

<...>

> If that's the case, just add your user account to the "audio" group, log
> out, and log back in, and with any luck JACK will run in realtime mode just
> fine.

Duh, I've made sure I was in the audio group well before posting.
Being in the group doesn't seem to do much. chmod +s jackd appears to
do the trick (although it may not have been a very good idea) - but I
still can't start jack from the GUI.

Cheerio,

Mick.

And this is supposed to be Ubuntu Studio? Shouldn't you file a bug report?