I just talked to Ben from Entertainment Book this morning and they have requested the trial membership links to be taken down from OzBargain. These are supposed to be targeted offers. Entertainment Publications (publisher of the Entertainment Book) offered those links to charity organisations to help them with their fund raising. Those links getting over-used (or "abused") by OzBargainers means that they'll need to shut down those offers, which means the charity organisation at the end would not be able to use it.
Therefore these are probably more of share-with-your-10-friends-on-Facebook offers, rather than share-with-other-10-thousand-OzBargain-pros offers.
Moreover Ben mentioned that some have posted comments on various hacks to redeem vouchers multiple times. Those are against their terms and conditions of use, and would have to be removed from OzBargain if Entertainment Book reports them to us.
They make fair points, although I guess this highlights the unintended consequences of online publishing. Even with ozBargain on board, these type of deals could go viral in other locations.