IDC reported today that in the third quarter of 2008, shipments of notebook computers into the U.S. market exceeded desktop shipments for the first time ever. Notebook PCs accounted for 55.2 percent of all computer shipments according to the research firm’s U.S. Quarterly PC Tracker report.

In spite of the deteriorating state of the U.S. economy, IDC reported that a record volume of 9.5 million notebooks were shipped in the third quarter, a figure that represents growth of 18 percent over the same period last year. Every notebook manufacturer experienced growth in the quarter, according to IDC, including both companies that sell notebooks exclusively (such as Toshiba) and those that sell both notebooks and desktops (including Acer, Sony, and Lenovo), with notebooks accounting for more than 65 percent of the latter’s U.S. shipments.

“The consumer market continued to be the top driving factor in the notebook offensive,” said IDC research manager David Daoud, “but the commercial sector played a critical role too. The consumer market has long favored notebooks, with mobile ratios exceeding the 70 percent mark.”

Asus and Samsung are making aggressive moves into this space, sensing new opportunities among a growing base of U.S. consumers who own multiple PCs, according to IDC’s analysis, with the potential for lower prices to stimulate demand and fuel continued market growth.

“Prolonged economic tension could have an adverse effect on the PC space leading to reduced growth,” said Daoud, “but the good news is that virtually every buyer considers PCs as must-have products and not secondary wish-list items.”