To put the worst possible spin on the news, as the
Wall Street Journal
did in Tuesday’s edition, domestic Mac shipments were down 1% year-over-year in November even as industry-wide PC sales rose 2%.

That was the data point that inspired Goldman Sachs’ David Bailey to cut his 2009 estimate — saying that “some nicks have started to emerge” in Apple’s growth curve and warning that the company faces “a tougher environment” in the first two quarters of next year.

To put the best possible spin on the news, as he is wont, Piper Jaffray’s Gene Munster skipped over November’s decline and focused on October’s Mac sales, which were up 28% year-to-year, thanks to the release of new MacBooks on Oct. 4. He expects that by the end of the quarter, Apple will have sold 2.5 to 2.7 million Macs, up 8% to 16% from the same quarter last year.

So why did November’s Mac shipments take that 1% hit? There could be several reasons.

I’d put my money on a global recession and the fact that Steve Jobs offered only one-day Black Friday discounts on Macs of 5% to 10%, while competitors like HP (HPQ) and Dell (DELL) were slashing already low prices as much as 50%.

Munster also blames the calendar, which offered Apple and the others 62.5% fewer premium shopping days this November:

“The month of Nov-08 included 5 fewer holiday shopping days (or days in November following Thanksgiving) than the Nov-07 timeframe,” he wrote in a report issued to clients Monday afternoon. “In other words, Nov-07 provides a tough comparison for the y/y Mac and iPod growth.”

NPD’s data suggests iPod sales of 18.5 to 19 million units for the quarter, according to Munster, down 14% to 16% year-to-year. He had been expecting iPods sales to be slightly slower than they were.

UPDATE: NPD analyst Stephen Baker gave Reuters a different set of numbers that suggest Apple’s notebook sales were actually quite strong in November, and that any weakness in Apple’s computer sales was concentrated in its iMac line.

Sales of desktops were down 20 percent overall, with Windows desktops sales falling 15 percent and Macs down 38 percent. Apple’s notebook sales, however, were up 22 percent in November, while Windows sales rose 15 percent.

“For notebooks, there is a little extra value to consumers (to buy Apple). For desktops I’m not so sure,” NPD analyst Stephen Barker (sic) told Reuters. “To me the real story is the iMacs need a refresh.” (link)

Apple (AAPL) fell 3.6% in Monday trading, to close at 94.75.

[Chart courtesy of the
Wall Street Journal
.]