If you want to run folding@home, buy a PS3.
Or a cabinet with about 10 Cell blades do, too. Each blade has two Cell BE, and quite honestly, I bet that thing would still wipe the floor with Nehalem. Until Nehalem becomes reasonably priced, I might change my opinions, but right now, you wouldn't even want to know the "estimated price" of a true 8-core, single Nehalem processor system... a 4-core Nehalem seems more reasonable, but is still quite out of reach for the mid-end users.