We kind of knew this anecdotally for some time but now there are some numbers to go along with it. PCs are still getting more popular as more and more people get online but the rate was slower than analysts expected:

According to the Quarterly PC Tracker Survey released today by IDC, overall worldwide PC shipments grew 2.7 percent year-on-year during the fourth quarter, with Gartner reporting a slightly larger 3.1 percent as part of its quarterly report. Both numbers missed the firms’ expectations, which IDC had predicted at 5.5 percent and Gartner at 4.8 percent.

Domestically, the news for the PC market was worse with shipments actually dropping by 4.8%.
Meanwhile, the Gartner report pegged Apple’s year over year growth at 23.7%, the highest of any computer maker.

Most analysts point to the iPad in particular and the looming tablet boom in general as being responsible for this boom.

Follow the money and it will lead you to the story.