According to Apple’s own PR page, it sold over 300,000 iPads in the US as of midnight Saturday, April 3, 2010. (So, technically, with stores opening or deliveries beginning around 9:00 or 10:00 am and assuming 16 hours of store sales, that is more than 18,750 iPads an hour or over 312 per minute or a little more than 5 per second.) This includes in store sales, pre-ordered iPads and deliveries to channel partners.
Interestingly, this is more than the approximately 270,000 original iPhones sold in the first 30 hours of availability.
iPad Notebook 