To my mind, they serve two very worthwhile purposes.
1. The large, very obvious paintwork, provides a constant reminder to drivers that they can expect cyclists in that lane. (And... who knows... they may even start looking elsewhere).
2. But, more importantly, they provide a lane where newbies can try riding with cars, and see that it's not as terrifying as they might think.
I'm scared tho. The copenhagenesque lanes (Swanston) are shocking. A good example of how (and where) not to do it. (Euan, that's one place I often ring my bell, to remind numpties getting out of their cars that I'd rather not run into them).
So yeah... if they don't carefully pick the lanes to trial them in, then they may not be seen as successful.
For mine, good candidates are some of the existing two lane carriageways in the CBD and inner city that currently service a lot of bike traffic. The ones that don't really have wide outer lanes, and/or bike lanes that are ridiculously narrow. Make the outer-most lane shared. The one which, I think, could perhaps be good is Rathdowne St into Exhibition St. I don't ride it often, but the bike lane really gets squeezed out there. So... make it shared.
(Of course, 40km/h limits would probably be better... but hey... I don't wanna jinx it).