When Apple announced the new iPad back in March, he spent a lot of time talking about the “post PC” world, a world in which tablets replaced PCs – particularly notebooks – for many users’ day-to-day needs, including web browsing, content consumption, and productivity. The iPad, he claimed, is the “poster child” for the post PC era. According to recent data released by NPD Display Search, he was right.

According to NPD’s Quarterly Mobile PC Shipment and Forecast Report, tablets – most notably the iPad – will account for an ever-increasing percentage of mobile computing sales over the next few years. By 2016, tablet sales are expected to surpass notebook sales for the first time, with the margin between the two increasing again in 2017.

According to NPD’s data, 208 million notebooks will be sold in 2012, compared to 121 million tablets (most of them iPads). By 2017, they expect notebook sales to clime to 393 million, whereas tablets will grow to 416 million. A key factor in the growth of tablet sales, they say, are mature markets like the North America, Japan, and Western Europe, where notebook penetration is high but tablet penetration is significantly lower.

NPD also predicted that the line between tablets and notebooks will become fuzzier over the next few years. In a trend that has already begun with some of the most recent models (including the MacBook Air), notebooks are trending sharply toward thinner, lighter form factors, SSD drives, and other features that increase portability and ease of use. Meanwhile tablets – which already pretty much have the portability and ease of use thing down – are trending toward the use of more powerful hardware and gaining more robust productivity capabilities.