But Apple did better than most. Daoud, in fact, saw bright spots in the dark clouds. "The 12.5% market share Apple had in the third quarter [in the U.S.] was a record high for the past several years," said Daoud. "And if you look at sales sequentially, they've actually benefited quite a bit."

By IDC's forecast, Apple grew U.S. Mac sales nearly 14% in the third quarter over the second. Daoud cited, among other things, Apple's strong back-to-school sales.

There's a chance that PC sales will rebound in the year's last three months as Microsoft rolls out Windows 8 and OEMs debut new hardware, including a plethora of hybrid devices that combine elements of both tablets and traditional notebooks.

Apple, of course, won't see any direct Windows 8 bump, but could reap rewards if the competition -- the Hewlett-Packards and Dells of the Windows side -- stumble with their offerings.

"This is a very challenging environment for everyone," said Daoud. "Globally, it's a perfect storm. In 2009, there was still very solid consumer demand for notebooks. That's what drove the market then," he said, referring to the last time Apple posted year-over-year declines in Mac sales. "Now, it's consumers, it's businesses, it's the OEMs themselves that are pulling back."