I too have seen innumerable buyer's groups go down in flames, some very quickly; however, from the standpoint of Australians and New Zealanders the idea has obvious appeal (since the shipping cost problem makes it so hard to make any money sourcing and selling in those markets.)
For what it might be worth, I would be willing to be the US end of an Aus/NZ buyer group, if putting together loads to ship would be a useful service. There are only so many product types I can directly source, but I do have warehouse space available, and could offer either a coalescing point where smaller orders from disparate suppliers could be grouped together (ideally to container size) to then ship over there, which would in theory dramatically reduce overall shipping costs. I could also do order fulfillment for "hands off" inventory, ie. items ordered from a US supplier, stocked in my space and reshipped to individual customers; however, as sexy as that idea sounds, I doubt I could compete with established fulfillment services on price -- only on level of service and options.