• by Erik Sass  @eriksass1, May 5, 2010

In the four weeks since the iPad went on sale on April 1, Apple has sold 1 million units of the new tablet-style computer, making this one of the biggest consumer electronics launches in U.S. history. Based, in part, on these figures, Forbes is predicting total iPad sales of 4 million in 2010, for an average rate of about 450,000 per month.

The iPad rush is good news for publishers looking to cash in on the growing popularity of e-readers with electronic editions of newspapers and magazines.

In the first month of sales, iPad users have downloaded an average of 12 apps per device, choosing from among an available pool of 5,000 apps. They have also downloaded a total of 1.5 million "e-books" from Apple's new iBookstore.

Two weeks after the iPad's debut, Zinio, which creates digital versions of magazines for print publishers, revealed that its "Magazine Newsstand and Reader" was the No. 1 free news app downloaded by new iPad owners -- besting competing apps from The New York Times, BBC News, NPR, The Wall Street Journal and USA Today. (The USA Today app is being underwritten by Marriott International through July 4.)

The iPad's success is a marketing phenomenon. It took about a year and a half for Apple to sell 1 million iPods, and two-and-a-half months for the company to sell 1 million iPhones after the device debuted in June 2007.

In the past, popular media-oriented consumer electronics devices like TV sets, VCRs and the Walkman all took several years to reach 1 million sales, and cell phones took about half a decade to get there, from 1982-1987. Amazon took all of 2009 to sell 1 million units of its new Kindle e-reader; Forbes is predicting further sales of 2 million units in 2010.