Apple CEO Steve Jobs recently roused some criticism for declaring the iPad to be the harbinger of a "post-PC" era. Market research firms seem to disagree with Jobs' proclamation; Gartner thinks he may be right, suggesting tablets are eating into PC sales, while NPD thinks slow PC sales have nothing to do with iPads. Forrester Research analyst Sarah Rotman Epps believes the transition started happening long ago, but the combination of advances in mobile technology, the increasing ubiquity of WiFi and mobile broadband, and consumers' increasing reliance on conducting official and personal business online means computing happens more and more with tablets and smartphones and less with a bulky desktop chained to a desk.

While popular wisdom seems to suggest that PCs will suddenly disappear as consumers flock to touchscreen tablets, Epps sees users using more kinds of computing devices which suit the given place and time. "Consumers own an increasing number of devices, including PCs, and they get very good at making tradeoffs in particular contexts," Epps told Ars. "79.3 million US consumers own three or more types of connected devices; eight million own eight or more types of connected devices," she said.

Epps, who focuses primarily on consumer product strategy, recently authored a report titled "What the Post-PC Era Really Means," in which she lays down an illumnating commentary on the current and future computing landscape. Jobs' reference to "post-PC" isn't new—Intel has been trying to usher in the era since at least 2005, and Ars has written about efforts from Microsoft, NVIDIA, and others to transition to a post-PC world since. Nor is post-PC a useless buzzword. "The post-PC era is real," Epps wrote in the report, "and its consequences will revolutionize computing product strategy."

The problem is that defining what post-PC really means is a lot more complex than suggesting tablets are in and PCs are out. There's a lot of life left in the PC business, Epps told Ars, even as tablets and smartphones increasingly grab consumer mindshare and dollars.

"The laptop form factor persists, for instance, but they start to act more like smartphones—flash memory, more sensors, and 'apps,'" Epps said, noting the popularity of the MacBook Air and Sony VAIO Z ultraportables. "Towers are still relevant for small businesses, professional users, gamers, and value-focused consumers. We're also seeing growth in the all-in-one category, because consumers like big screens."

What defines the post-PC era is a shift in four fundamental qualities that Epps identified as particular to traditional PC computing. Namely, traditional PC use was stationary, formal, at arms length, and relied on abstracted interaction. A user sat down in a particular spot, usually a desk, for a pre-defined period of time, and used a computer by entering text via a keyboard or manipulation abstracted symbols via a mouse.

Post-PC computing, in contrast, is ubiquitous, casual, intimate, and physical. Devices are always on and always at the ready, used increasingly for various combinations of work and personal use, used as much in the living room as the bedroom, and rely on close physical interactions (think fingers on a touchscreen, but that could change in the future to facial recognition via a Kinect-like input).

This transition has been happening over the last decade, as users become reliant on online services—imagine not being able to check Google Maps to find your way to a distant location, consult Yelp for the nearest source of burritos, or transfer funds from savings to checking right from a Web browser. WiFi and mobile broadband untethered such activities from the desk, and smartphones freed them further by putting them in your pocket. And the increasingly blurred line between work life and home life has created new generations of users that expect to shop for a CD on Amazon or analyze the latest quarterly sales figures pretty much any time of the day.

While these factors make it clear that we are indeed living in a post-PC world, PCs won't disappear overnight—no matter how many millions of iPads Apple sells in any given quarter. Cloud services will need to expand and offer better reliability. Mobile broadband networks still have areas of poor or no coverage. And some users will simply find a laptop or desktop suits their needs better than mobile devices, while others will use multiple devices—a laptop in the den, a tablet in the bedroom, and a smartphone in the pocket.

"In the post-PC era, the 'PC' is alive and well, but it morphs to support computing experiences that are increasingly ubiquitous, casual, intimate, and physical," Epps wrote. In other words, PCs will happily co-exist with mobile devices like tablets for the time being. While tablet buyers may not be buying new PCs in the next 6-12 months, users will hold on to their current PCs which work "well enough."

You can expect vendors to expend increasingly more time and effort into building "curated computing" devices that target specific needs with increasingly mobile and specialized form factors. And one day, our kids will mock a "PC" collecting dust in a corner of the basement. While we are already living in a post-PC world full of iPhones and Droids and Xooms, that day isn't quite here yet.