Reports: Apple slipped to 4th place in Q4 U.S. sales by Philip Elmer-DeWitt @FortuneMagazine January 17, 2008, 1:13 PM EDT E-mail Tweet Facebook Google Plus Linkedin Share icons Acer, the Taiwanese computer manufacturer that acquired Gateway Inc. last year, has as a result overtaken Apple (AAPL) in both U.S. and worldwide computer sales, according to preliminary reports issued Wednesday by Gartner and IDC. Although the two market research firms show Apple’s domestic computer sales in the Christmas quarter up roughly 30 percent from last year — outpacing the industry average by better than 3 to 1 — Apple’s share of the market actually fell during those three months. According to Gartner, the Mac now has 6.1 percent of the U.S. market; according to IDC it’s 5.7 percent. That puts Apple in 4th place behind Dell (DELL), HP (HPQ) and Acer in U.S. personal computer sales. In October, Gartner and IDC estimated Apple’s 3Q share of the U.S. market to be considerably higher: 8.1 percent and 6.3 percent, respectively. See here. In worldwide PC sales, Apple doesn’t make the top five in either research firm’s report. These results would seem to contradict analysts’ predictions of blowout Christmas sales for Apple. Earlier this week Piper Jaffray’s Gene Munster estimated that 2.3 million Macs may have shipped worldwide in the quarter, representing year-to-year growth of 43 percent. Gartner’s and IDC’s results are preliminary and could change when the manufacturers release their sales figures. Apple is scheduled to announce it’s quarterly results next Tuesday. Below the fold: Gartner and IDC charts of U.S. computer sales.