appmodo.com has an article named "Shipping Has Begun, iPad Pre-Orders on Their Way" by Mary Ann Neder.
Good news folks! Looks like iPad WiFi pre-orders have begun shipping from Shenzhen, China using UPS Expedited service. Don’t hold your breath about getting your newest toy in before Saturday though, as Apple has worked with carriers in the past about withholding delivery for products until a certain date.