20%? Isn't that a standard employee discount just about anywhere you work? 50% would be a bit more enticing.
HP should really give them to employees, considering the uphill battle any tablet manufacturer has against the iPad, they need all the buzz they can get. Why spend money on marketing, when a satisfied customer's posts will do far more to get people to buy the product.
They'll probably spend millions marketing this thing, if they just gave away the tablets for free, they'd have more success.