Consumer behavior is changing even more rapidly than you might think. In the past couple of weeks, my colleague Samantha Jaddou and I have been analyzing the data for the US version of our annual global series, “Understanding The Changing Needs Of Consumers.” We are seeing not only a decline in the number of US consumers with a computing device (a PC, laptop, or netbook) but also a drop in the amount of time that consumers spend on traditional media like watching TV (on a TV) or reading newspapers or magazines.

One of the biggest revelations in this year’s data was the change in attitude of consumers — particularly younger ones — toward the Internet. Since we started tracking this information in 1997, we have only seen the amount of time spent online increasing. But Forrester’s 2012 data shows that US online adults are now reporting a decline in the amount of time they spend using the Internet compared with 2011 and 2010.

What’s going on? Our analysis revealed that “being online” is becoming a fluid concept. Consumers no longer consider some of the online activities they perform to be activities related to “using the Internet.” In fact, given the various types of connected devices that US consumers own, many people are connected and logged on (automatically) at all times. The Internet has become such a normal part of their lives that consumers don’t register that they are using the Internet when they’re on Facebook, for example. It’s only when they are actively doing a specific task, like search, that they consider this to be time that they’re spending online.

Which leads to another interesting question: How do all the devices they own play together? We found that the user experience defines device preference. For example, the majority of US online consumers still rely on their main computer (either a laptop or a desktop) to perform serious online tasks, such as shopping, banking, or booking travel — even when they have access to a smartphone or a tablet. Engaging with social media is the only activity where tablet owners are equally likely to use their tablet or their mobile phone, although even then the laptop remains the No. 1 device of choice.