Since the launch of Apple's iPad last year, tablet devices have quickly become a popular way for consumers to engage long-form online content, regardless of whether they're at home or on the go.

Since the launch of Apple's iPad last year, tablet devices have quickly become a popular way for consumers to engage long-form online content, regardless of whether they're at home or on the go. According to a new report from RISI, tablet market penetration is expected to continue to grow, which further emphasizes the importance of mobile content marketing efforts.

In 2010 alone, more that 15 million American consumers purchased tablet devices. Over the next few years, tablet sales are expected to skyrocket, with as many as 190 million Americans owning the devices by 2015. RISI's conservative estimates predict that at least 120 million tablets will be in the hands of consumers within four years.

This bodes well for businesses that leverage online news content, with RISI predicting use of traditional print newspaper and magazine usage will decline by at least 20 percent in favor of internet news sources. Marketers may find news content marketing helps them engage growing tablet audiences.

A separate study conducted by Barkley marketing agency, Service Management Group and The Boston Consulting Group also highlights the growing usage of mobile devices, such as tablets, especially among millennials. Half of this demographic uses mobile devices to aid their online research and shopping.