"I've been in a lot of allegedly 'mixed' sessions where an unaccompanied (and often unaccomplished) singer will drone on for twenty-odd verses, with choruses between each verse, ... "

Unfortunately, 'Mandotim' I have to agree with you, even though I am a keen fan of the well-sung ballad.

At far too many of the singarounds I attend the length of the song seems to be inversely proportional to the talent of the singer. I am convinced that quite a few indifferent (or just plain poor) singers deliberately choose the longest songs that they can find so that they can 'hog' as much of the session as possible. They then have the cheek to moan when the singaround organiser fails to pick them for the next round!