Apple stores in 10 countries, including the U.S., will be opening at 8 a.m. on Friday to accommodate the crowds. Several major retails, such as Best Buy, RadioShack, and Wal-Mart will be selling the tablet as well. From the WSJ:
The Cupertino, Calif., company said in recent days it had sold out of its allotment of iPad preorders, saying that interest among its customers was "off the charts." The company has since said new preorders would take about two to three weeks to ship to customers. Piper Jaffray forecasts Apple will sell more than a million new iPads on Friday, up from around 300,000 when the original iPad went on sale in April 2010. Several financial analysts are predicting sales of multiple millions over the first weekend.
By the way, Apple stock broke through the $600-a-share mark in today's trading before sliding back. It's now at $583.