i think the idea of a progressive sales tax is interesting and should be investigated.
the goal, i think, of taxing people is to find some way of making sure that we all contribute to the well-being of society, and taxes -- which fund things like roads and schools and dams -- are one way of going about that. it makes senese that people at the top of the income ladder pay more because, 1) they can afford to, and, 2) society has been good to them, so they do, in a senese, "owe" it to their fellow citizens. also, you don't see too many sons and daughters of Greenwich, Beverley Hills, or of members of Congress (of course not all) serving in Iraq, as our armed forces tend to skew heavily towards the middle and working classes. we all have to pull our own weight, but in different ways and in accordance with our abilities.
a consumption tax, if applied fairly, and in my opinion it should be something similar to a VAT where non-essentials are taxed more heavily than essentials, might be a good way to ensure that the very wealthy pay their fair share (as they so often don't, with off-shore holdings and a team of lawyers ready to beat the tax codes ... and that's just individuals, dont' get me started on how corporate America is always 3 steps ahead of the IRS ... it's sickening and sad).
it does make sense, for example, to heavily tax a speedboat but not a loaf of bread. i suppose what becomes difficult is to determine what becomes considered a luxury and what is a necessity.
i dunno. it's an interesting idea, but the implementation of it sounds rather difficult.