The changes in Apple’s new Mac OS X Lion, released Wednesday, start with the way people get the updated operating system. It’s not available on an installation disc or from a traditional website. It’s a $30 download from the Mac App Store — complete with its own “Buy App” button.

Features of the overhauled Mac OS X include a “Launchpad” view that lays out app icons in an iPad-style grid. Users will be able to double-tap the Mac trackpad to zoom in and out, as if they were using an iPad or iPhone. The operating system can quickly switch apps and sites to full-screen mode, as if running them on a handheld device.

This is the computer, updated for a world that revolves around mobile technologies.

The start screen in Windows 8, expected to be released sometime next year.

It’s just the start. Microsoft will be following a similar path with the next version of Windows, overhauling the default interface in a nod to the rise of tablet computers and mobile devices. Windows 8 is a big gamble, with the risk of alienating or at least shocking longtime Windows users, even though the traditional desktop will still be an option.

One lesson that Microsoft might learn from Apple’s Lion is that it’s possible to go too far.

Exhibit A: Inverted scroll. Here’s how Walter Mossberg describes this change in Lion in his Wall Street Journal review: “Instead of moving the top of a page upward by dragging the scroll bar down, or moving your fingers downward on the touch pad, you do the opposite—you just push the page up. A scroll bar appears only while scrolling. (Older programs may still have the traditional scroll bar.)”

In other words, it’s the same way we interact with content on a mobile device. Except it’s on a computer, where we’ve been doing things in a completely opposite way for pretty much forever.

David Pogue of the New York Times says it takes a couple days to stop scrolling in the wrong direction. Already there are articles explaining how to revert to the traditional technique.

No doubt this is part Apple’s plan to simplify the way we interact with devices, creating a common way of navigating content on our many machines. Possibly it will make more sense in the long run, as the lines blur between different forms of operating systems and devices.

But in the meantime, this is all starting to feel a little too trendy — and maybe a little too much.

Update: Although the Mac App Store is the only way to buy Lion at launch, Apple will make the software available next month on a USB drive for $69.

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