It’s no secret, at least no longer, that Apple’s iPad tablet computer is adversely impacting PC sales. Apple’s sold 25 million of the devices. That’s 25 million units of a product that did not even exist some 15 months ago.

It may be no stretch to suggest that the iPad single-handedly killed the faddy netbook buzz PC manufacturers were so thankful for just a few quarters ago. HP and Dell are even among those said to be suffering, according to a recent Bloomberg Businessweek report. There’s, in fact, a term for iPad PC sales cannibalization now: the iPad effect. Even Gartner has commented on the trend.

Some say the iPad’s effect is overblown. I say it isn’t. But just why is the iPad proving so popular, including for business users?

Is it because the iPad is a sexy gadget many wish to flaunt at the local coffee house or board room meeting? Hopefully not.

Is it because the iPad is typically less expensive than a full-blown computer? That’s certainly not hurting iPad sales, especially during challenging economic periods when organizations are tempted to lower technology costs.

Is it because the iPad is an easy-to-use intuitive computer? That helps, certainly.

But the primary reason iPads are selling so well and displacing other technology investments is, I believe, because they combine several needed and critical elements into a single flexible platform that easily performs double duty. Don’t forget small businesses constitute the lion’s share of the U.S. economy. There are a lot of them out there.

While many large enterprise organizations are busy performing exploratory iPad studies, studying iPad specifications, preparing iPad task force project schedules, organizing steering committees whose purpose will be to select a committee to determine an iPad’s business capabilities and attempting to strategically tie an iPad’s functionality to core business objectives and calculate corresponding quarterly return on investment ratios, small businesses are simply deploying the devices. And, they’re finding they work and perform really, really well.

My consulting firm has seen businesses-across a vast spread of vertical markets-adopt the iPad with unanticipated rapidity. They’re doing so because the business owners, managers, technicians, field service personnel and other employees desire a single device that can leverage RDP connectivity in the field to connect them to a mainline business application housed on a preexisting terminal server.

They’re tapping the iPad’s optional built-in 3G connectivity to provide newfound connectivity in the field at reasonable cost. They’re leveraging the device’s ability to access Exchange-powered email, calendaring and contacts wherever they might be without having to lug around a laptop. They’re discovering readily accessible applications available at low cost that better enable their businesses to manage daily operations and challenges.

These SMB owners and employees are enjoying a simple factor others may be overlooking in importance: iPads are convenient for personal tasks, too. Today’s workforce blurs lines between personal time and professional responsibilities. In large enterprises the lawyers and HR reps are quick to get involved determining what constitutes fair use for this, whether an employee can be tasked with performing specific work-related tasks at night without being subjected to overtime requirements, what constitutes appropriate business-use for this corporate-provided device, etc.

Small businesses? They don’t care. They’re more agile. They’re more willing to just do something — anything —  in a crappy economy that rewards fresh thinking, ingenuity, and elbow grease. They just want a device they can use to sell an HVAC system in a client’s home, track down the trim package or price of a new car on the auto lot, prepare an estimate at a client site, provide patient care in a suburban medical office (with all the HIPAA-protected data on a secured terminal server) and to perform other common business responsibilities during the workday. After hours, users can use their iPads to access personal email, Facebook, and the Internet and maybe read a book (via the Nook, Kindle or iBook apps) or even to stream a Netflix movie. The iPad fulfills all these tasks exceedingly well.

Skeptical? Just ask Acer’s former CEO. I think he’ll tell you Acer missed the boat by not working more aggressively to invest in tablet technologies itself.

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