Photo: Apple Inc.

Apple's (AAPL) surprise announcement Tuesday of four new or updated product lines -- iMac, MacBook, Mac mini and a touch-sensitive "Magic Mouse" -- does at least three things:

1. Builds on the momentum created by the blowout earnings announced Monday
2. Gives customers a reason to reconsider Apple's desktop machines
3. Keeps the press from writing about Microsoft's (MSFT) Windows 7 -- set for release Thursday -- for at least another day.

The second point was underscored in a note to clients issued Tuesday afternoon by Piper Jaffray's Gene Munster. He points out that Apple achieved an 17% increase in computer sales last quarter despite fighting the "headwind" of desktop machines that had grown increasing long in the tooth. Desktop unit sales were down 16% year over year last quarter, compared with an astonishing 35% increase in MacBook sales.

The new machines -- especially the thinner, faster iMacs -- could change that.

"In other words," writes Munster, "the headwind that existed in the Sept. quarter due to aging Mac desktops has now turned into a tailwind for Mac units in the Dec. quarter."

The best place to learn about the new machines is probably Apple's own website. We're particularly fond of the little video industrial designer Jonathan Ive recorded about the new iMacs, pasted below the fold.

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