We all know that Apple has been selling the iPad for more then a day if you count pre-orders, etc. However, Mercury News has a nice article estimating that Apple sold over 700,000 iPads today.
That is a mind boggling number of units on the first day, and it illustrates the pent up demand exactly for a device like this. Steve Jobs made everyone wait until they had something that they felt would be a game changer, and the sales numbers seem to illustrate he's succeeded.