The new iPad doesn’t hit shelves until March 16 but Apple says it’s already seeing high demand for its tablet computer. Hayley Tsukayama reports:

Pent-up demand for the next iPad has sent customers clicking the “pre-order” button on Apple’s Web site in droves. In a statement to USA Today, Apple said that customer response to the new tablet has been “off the charts” and confirmed that the pre-order devices have sold out.

As of this weekend, buyers will have to wait two or three weeks to get their hands on the tablet — or brave the crowds at Apple stores. The lines for Apple launches are historically jam-packed. Because the company is rolling out the devices in Europe and Asia at the same time as the North American launch, the new iPad launch is on track to be one of Apple’s largest-ever device debuts. Apple, which has sold about 55 million iPad devices to date, is expected to sell at least that many by the end of 2012.

So it’s probably no surprise that Slashgear reports that they’ve already come across two people who’ve been camping out at London’s Regent Street store. According to the report, the two men — Ali and Zohaib — started the iPad line at the store on Saturday, packing folding chairs and warm clothes.

The new iPad, which adds a sharper display, faster processor, access to 4G LTE networks, a better camera and voice dictation to the tablet, will be in stores on Friday, March 16. The WiFi version starts at $499, and the 4G version starts at $629, not including the data plan.

Weighing whether to buy an iPad or one of its Android- or Windows-based competitors? Hayley Tsukayama explains how they compare to one another:

Apple added better cameras, 4G LTE and made a couple of significant internal upgrades to the tablet, all with the aim of making it a better machine for content creation.

It also takes on a wave of competitors who banked on offering one or more of those features in order to get a niche of customers that prized one or more of those features enough to look off the beaten path at iPad alternatives. Adding 4G? That’s a punch in the eye for tablets like the HTC Jetstream, T-Mobile Springboard or Galaxy Tab 10.1, which have been able to argue their network speeds as a selling point against the iPad 2.

Apple even took a step to take on its low-priced rival, the Kindle Fire, by dropping the price of the iPad 2 by $100 to a $399 price point. That’s definitely still expensive, but it may be enough to sway people who were considering the $199 Kindle Fire but want a fuller tablet. With a cheaper iPad, Apple’s main competitor for the new iPad is probably itself.

The iPad still has its vulnerabilities, though. Samsung is still arguing that its new Galaxy Note 10.1, with its S-Pen stylus beats any version of the iPad in the content creation game. And Apple still hasn’t added—and isn’t likely to— say, an SD card slot or HDMI port, choosing instead to challenge tablets with more ports (Toshiba Thrive, Acer Iconia) or expandable memory (most Android-based tablets) with iCloud storage and streaming through Apple TV. And the company still hasn’t introduced a smaller tablet at a time when the 7-inch form factor seems to be catching on with tablet consumers.

There’s also always the possibility that Microsoft, with its plans for Windows 8 tablets, will be a challenge to Apple in the enterprise market — an area where Apple has been making a big push. According to a report from The Post’s J.D. Harrison, there’s not much in the new iPad that will tempt businesses, but the introduction of Microsoft Office on a tablet has the potential to be very interesting to businesses.

Overall, however, Apple’s managed to stay just enough ahead of the rest of the market to stay the strongest competitors in a field that’s growing more crowded every day.

Despite all the buzz Apple receives for being first in the tablet computing arena, at least one innovator may have beaten the firm to envisioning the future. Michael S. Rosenwald reports:

For [Roger] Fidler and colleagues who knew him back when he dreamed the future, the video’s resurfacing generated exhilarating but sore memories — and lots of thorny questions: What if their lab hadn’t been shut down by shortsighted corporate bean-counting? Is Fidler getting enough credit, or even any credit? Did Apple (ahem) steal the idea?

Or had Fidler’s crew simply planted the concept of this most fantastic innovation into the public mind all those many years ago? This last one, it turns out, is the linchpin question in an epic patent battle between Apple and Samsung, an emergent rival in the tablet market. And of all the wonder and what-ifs, it’s the question that has catapulted Fidler from his peaceful academic life to the center of a global legal war.

Apple is suing Samsung, alleging that the Korean company copied its iPad design. And Samsung is defending itself, in large part, by using Fidler’s video-gone-viral, saying it proves the design was already in the public domain and is thus not patentable. Fidler is bewildered. He cherishes his sleek white iPad, but most unexpectedly he’s quietly siding with the enemy of a dead man he reveres.

“I never would have anticipated this would become such a big issue all these years later,” Fidler said. “All of this has certainly surprised me.”

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