According to a study conducted by The NPD Group, the answer to that question is web browsing and Facebook. More than 20% of those polled by The NPD Group indicated that they’re surfing the web and using Facebook less on their PCs because they’re engaging in those activities on their smartphones and tablets instead.

Don’t count the PC out yet

The shift from the PC to mobile and tablet devices is obviously very real, and meaningful, particularly in the case of Facebook, which is seeing the gap between PC users and smartphone users narrow.

But it would be premature to write off the PC as a thing of the past. As The NPD Group notes, “consumers are still using their computers for many of the core PC-centric activities.” 73% of PC owners still use their PCs to browse the internet, for instance, compared to 61% and 53% for smartphones and tablets, respectively. So there’s still a huge market for serving consumers accessing the internet through a desktop experience, something that even the most mobile-savvy and mobile-centric companies are clearly aware of.

Serving consumers wherever they are

Consumer behavior is, of course, inherently difficult to predict. While it seems all but certain that consumers will continue to increase their non-PC engagement with online services, it’s too soon to make assumptions about specifics. On this point, it’s worth noting that 21% of consumers have an internet-connected television, and The NPD Group says that more and more of these consumers are using those televisions to consume content from services like Netflix and Hulu.

So how should businesses react to these shifts and plan for the future? First, it’s important for each company to evaluate their specific audiences and how their consumption habits are changing. As John Buffone of The NPD Group observed, “Despite these shifts in behavior, computers will remain the fundamental content creation device in consumer’s tool box for many years to come. Consumers, however, are switching their entertainment-centric behaviors to tablets, smartphones, and connected TVs at warp speed.”

The key take-away: some kinds of businesses will be affected more than others, sooner than others. But all businesses should recognize the fact that they’re operating in a multi-device, multi-platform world, and to maximize the value received from each customer relationship, experiences across numerous devices and platforms will be required.