I just hope that these Natal and the Arc (it's still called that, right?) don't go the way of hundreds of other peripherals in the past. I honestly think that the only way these two new technologies can succeed is if Sony and Microsoft practically give them away for almost free. Unless they catch on like Wii Fit (I've never seen one in person outside of the store) or Guitar Hero (I've only seen two people that own a version of it), they can easily become high tech, innovative, failures.
Historically, peripherals don't even reach 20% of console owners (Going from memory. I even picked a higher attach rate percentage in favor of non pack-in peripherals). Are the times changing?