I think there are a few ways it could pan out. I don't see it attracting much of the casual non console owning audience as there is a cheaper, more well known option already available in the Wii. That said, it could prove to be the feature that finally makes some of the more casual PS2 owners finally upgrade to a PS3 (those who haven't already bought a Wii anyway), although perhaps not at its launch price. A year or two down the line (and a price cut later) then I definately see it attracting some of the PS2 owner crowd but I don't ever see it pulling in new non-console owning people as the Wii has (and continues to do).
Perhaps it will have a little better luck with non-PS3 owners who enjoy the more core games as (IMO) it is currently the best motion control device for core game support (KZ3, Socom 4 ect). I think Natal will prevent many 360 owners from picking up Move and a PS3 but it could attract some of those who currently don't own either a 360 or PS3.
