Apple has announced the ship date to be April 3, 2010 for iPad in the USA, and begins to take pre-orders on March 12, 2010.
According to Apple’s January 28th announcement, they will released the iPad in stages. The WiFi only versions are expected to release 60 days from the announcement date (approx. March 30th), then the versions with WiFi+3G was to come 30 days (approx. April 29th) after that.
So based on the above understanding the April 3rd ship date should be for the WiFi only versions, and the versions with WiFi+3G are expected 30 days after that; some time beginning of May (approx. May 4th), just in time for Easter.