I think I was reading this document ... The Aust Road Authorities and Bicycles Rules - http://www.woj.com.au/AustRoadRulespts1-21.pdf
Here's a couple of interest ...
2 Abreast ... seems like it's totally legal .. not sure where I got that it 'depended' ... perhaps from conversations with police officers I know.
However, I maintain that common sense is needed and exercising this right is not always the best choice in my opinion. I'd personally like to see this rule changed. In the meantime though it should become a commonly known rule for all road users.
Rule 151 - Riding a motor bike or bicycle alongside more than
1 other rider
(1) The rider of a motor bike or bicycle must not ride on a road that
is not a multi-lane road alongside more than 1 other rider,
unless subrule (3) applies to the rider.
Offence provision.
Note Bicycle, motor bike and multi-lane road are defined in the
dictionary, and rider is defined in rule 17.
(2) The rider of a motor bike or bicycle must not ride in a marked
lane alongside more than 1 other rider in the marked lane,
unless subrule (3) applies to the rider.
Offence provision.
Note Marked lane is defined in the dictionary.
(3) The rider of a motor bike or bicycle may ride alongside more
than 1 other rider if the rider is:
(a) overtaking the other riders; or
(b) permitted to do so under another law of this jurisdiction.
Note Overtake is defined in the dictionary.
Roundabouts ... multi-lanes means if you are in the outside lane in a bike you must give way to exiting traffic if necessary.
Rule 119 - Giving way by the rider of a bicycle or animal to a
vehicle leaving a roundabout
The rider of a bicycle or animal who is riding in the far left
marked lane of a roundabout with 2 or more marked lanes, or
the far left line of traffic in a roundabout with 2 or more lines
of traffic, must give way to any vehicle leaving the roundabout.
Offence provision.
Note 1 Bicycle and marked lane are defined in the dictionary, and vehicle
is defined in rule 15.
Note 2 For this rule, give way means the rider must slow down and, if
necessary, stop to avoid a collision — see the definition in the dictionary.