This turned up on another message board.

"Alternate drop" service is a way of handling a banquet (such as a wedding reception) that seems to be peculiar to Australia. The hosts choose two (sometimes three) different dishes, say chicken & beef. 50% of the dishes will be chicken & 50% beef and they are served alternately around the table. This is apparently cheaper than having the guests choose between chicken & fish in advance, which is they way it's usually done in the US. "Alternate drop menus include two dishes served alternatively around the table. Guests don't actually order their choice of dish, but the idea is that they are free to swap with their neighbour if they wish. It's a way of giving your guests some flexibility without going to the expense of a full course choice."

Most non Australians were flabbergasted. They'd never heard of such a thing and couldn't imagine asking strangers to trade meals. The Australians were also flabbergasted. Alternate drop is so common that it's considered a given and "if you dont eat something there is always someone there who will swap with you! Every wedding we have been to have done the same thing, and no one has ever complained!" and "I hate it. If you get your preference it's okay, as long as you don't get bothered by the longing looks or whimpering of those who didn't. But if you don't it can be awkward at best, and mean going without dinner at worst."

So--is "alternate drop" common elsewhere?