Uh, I think Bill Gates proved that hardware is virtually useless without software applications that enable people to achieve some objective.
So which killer app came first? Sketching pictures of animals on the walls of the cave or cursive notation taken while sitting in a boring project management meeting?
The burned piece of charcoal Gog discovered he could use to make marks with or a pictorial memory or thought in Gog's mind he had no way to convey to others until he downloaded those thoughts onto his Charcoal Drafting Stick R1.0 and started sketching on the walls of the cave?
SketchUp on the Tablet PC replicates one of mankind's oldest experiences; the tactile experience of holding a tool in the hand. A tool such as a pencil and paper, a tactile experience that results in an epiphany when software like SketchUp is used on a Tablet PC.