This subject has been totally nailed by Jennifer Hewitt's article in the AFR. She just blows the whole thing apart. It's really just a stunt by the ALP to show that they are being "fair" and to feed the typical ALP hatred of anyone who has money. But it will cost EVERYONE heaps to implement, increase complexity, tax the wrong people and won't raise much money anyway! It's totally stupid anyway because any meaningful change should be coordinated with pension reform and broader issues and should be prospective in nature.
