Notebook sales growth goes negative. Can we blame the iPad yet?

Thursday night, just as a tornado -- or something like it -- was knocking down the trees that grow in our Brooklyn neighborhood, Morgan Stanley's Katy Huberty issued a report to clients with a chart (copied above) graphing the damage done to the notebook PC market over the past eight or nine months. "Tablet cannibalization" -- chiefly by Apple's (aapl) iPad -- is at least partially responsible, she suggests. Her evidence:

  • NPD data showing that after six months of decelerating growth, U.S. retail notebook unit growth fell 4% year over year in August, marking the first time those numbers had actually gone negative.
  • Similar data for the first week of September showing that units fell 4% year over year again.
  • BestBuy CEO Brian Dunn's widely repeated remarks in the Wall Street Journal that "internal estimates showed that the iPad had cannibalized sales from laptop PCs by as much as 50 percent.” [UPDATE: Dunn is backing off those remarks. See here.]

Huberty concludes: "We expect tablets to continue to pressure PCs as more vendors launch products (e.g., Dell Streak and Samsung Tab) and Apple expands its iPad distribution."

[Follow Philip Elmer-DeWitt on Twitter @philiped]

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