Apple's iPad has hit the one million mark. On Monday, the Cupertino, California-based company announced that number of units have been sold in the tablet's first 28 days, and that 12 million applications and 1.5 million digital books have downloaded.

Apple CEO and co-founder Steve Jobs said in a statement that one million iPads in 28 days is "less than half of the 74 days it took to achieve this milestone with iPhone." He also noted that "demand continues to exceed supply." Apple's online store has said there's a five-to-seven day waiting time for iPad deliveries, and Best Buy is only offering the product at some stores.

300,000 3G Units Estimated

Some industry observers are predicting sales of five million or more for 2010, even though launch day was on April 3 for the Wi-Fi model. On Friday, the 3G version went on sale. Piper Jaffray analyst Gene Munster has estimated over 300,000 of the 3G units were sold over the past weekend.

In addition to the more than 200,000 iPhone or iPod Touch apps in the company's App Store, more than 5,000 new, third-party apps for the iPad have been created.

The selling frenzy for the iPad could indicate that the tablet category has at last come alive, or it could just be about the iPad. The iPad builds on previous Apple successes by using the iPhone operating system and allowing the same apps to be used.

One key competitor was thought to be the Windows 7-based HP Slate, which was showcased at the Consumer Electronics Show in January by Microsoft CEO Steve Ballmer. HP had also been releasing a stream of videos and specifics about the tablet, and a launch date was expected sometime in the middle of this year.

'Not a Passing Fad'

But developments last week indicate that the iPad may not have to confront a major competitor quite yet. According to news reports, HP has decided not to release Slate in its current form. There are also reports the computer giant decided Windows 7, with HP's touch overlay, was not the right combination to take on the iPad.

Last week also saw the purchase of struggling smartphone maker Palm by HP for $1.2 billion, and there are now expectations that HP will use Palm's webOS for a reworked Slate.

Michael Gartenberg, partner and analyst at the Altimeter Group, said that the iPad's million mark is all the more impressive when one recognizes that "it's hard to sell a million of anything."

The milestone, he said, means that the iPad "is not a passing fad," and that Apple "has broken open the tablet category."

The bottom line about HP, he said, is that "we just don't know what they intend to do." Gartenberg noted, however, that Windows 7 is "designed for large screens, keyboards, and mice," not for tablets.

But HP's situation may not leave Apple as the only major tablet player for long, he said. "Keep your eye on Android," he said, particularly given that Google has said future releases of its open-source operating system will be optimized for tablets.