The NW-HD1, (they really need a far sexier name), is smaller and lighter than the iPod, and a bit bigger than the iPod Mini and holds 20G worth of music. As for battery life, it boasts a 30 hour rechargeable battery. Price? Looks to be about AU$800 with an August-ish release.
Will I be cashing in my beloved 30 Gigger (iPod) for one of these? No.
Will it offer some healthy competiton for Apple? Yes.