What a sensible and well-informed thread, which brings up some excellent points. Thanks Acorn4 and Joe for starting it off.

A well-run singaround should not need "rules" - especially if the host knows what he/she/they be doing! - but certainly the Code Of Conduct interpretation is sound as a guideline.

Gazza2 - yes, I too have attended singarounds very much like this, which is why I despair of the recent trend at most festivals to treat singarounds and the like as a poor relation, often just slotted in at an awkward time or at an uncongenial or plain unsuitable venue just to "tick the box" on the programme page...

Too many festival organisers seem (whether knowingly or otherwise) to persist in engaging singaround hosts who "hog it" or use the event as a vehicle for their own band or mates to try out new songs or do a mini-concert.
And - even worse - are the festivals who advertise a Big Sing which is nothing less than a parade of booked guest artists who already have plenty of concert or other exposure during the festival. And many festivals advertise a "Folk Club"-cum-singaround which has (again) timed 20-minute booked-guest feature spots every 40 minutes or so, leaving absolutely minimal time for other singers. Then, if we're lucky, there might be an isolated singaround that's genuinely fairly run, but has so many potential singers that it only gets round once and is over after a couple of hours so that the room can be used for yet another mini-concert or whatever. Like Guest Jerry, it is often the case that the parking ticket will expire, and it simply isn't on to wait two hours to get a turn especially when you've travelled a long way to get there (as opposed to having just fallen off the campsite and turned up late at the singaround).

This is not just idle sniping and griping, for I speak from experience. Experience as a regular singaround attendee, but also practical experience of running/hosting singarounds etc - and over the past 20 years receiving plenty of positive feedback for a well-run singaround or session.

The marks of a good singaround?
Hosts treating fellow-singers with respect rather than as an annoyance that gets in the way of one's own party-piece.   
Being flexible having observed the mix and dynamics of those who've turned up, being prepared to take things as they come to some extent but also to have a grasp of purpose and structure to the gathering without being over-didactic...
Not announcing "short songs only for this round please" then proceeding to sing a lengthy ballad yourself or allow your mate an extra turn.

I run a monthly singers' club, and I know it is perfectly possible to get around the circle at least four or five times, sometimes even six, during an evening, and also allow for some in-between-songs information exchange. So why do so many singarounds start late, then turn into an extended chat session and finish early or predictably on the same song every week?

One final point (unrelated to the above) - in a mixed session, an instrumentalist or duo/trio/etc can often get away with a medley of up to three tunes (with repeats!), yet a singer is frowned on when he/she performs a medley of two short songs that actually go well together... (and often lasts half the time of the aforementioned tune-set).
Hog-it means hook-it!

OK, I'll get off me soapbox now!