Apple giveth, and Apple taketh away. As it released Mountain Lion through the Mac App Store Wednesday, the company simultaneously removed Lion from the store: You can't find Lion if you search for it, its no longer listed as one of Apple's apps in the store, and even the direct Mac App Store link no longer works.

If you're already contentedly running Lion on your eligible Macs, or if you eagerly downloaded and installed Mountain Lion already, Lion's removal from the Mac App Store is no big deal. For certain users, however, Apple's removal of the Lion installer from the store could become problematic.

Several Macs can run Lion, but not Mountain Lion. These include 2006 iMacs, the 2008 (original) MacBook Air, Late 2006 through Early 2008 MacBooks, 2006 15-inch and 17-inch MacBook Pros, the 2007 Mac mini, 2008 Mac Pros, and the 2006 and 2008 Xserve models. If you still use one of those older Macs, and youre running Snow Leopard, Apple's decision to pull Lion puts you in a bit of a pickle. Though your machine can run Lion, you have no obvious way to get it on your Mac anymore.

What's more, your friends may not be able to help you, even if they have already bought Lion from the Mac App Store: The app is completely gone from the store; in Macworld's testing, the installer doesn't even show up in the Purchased tab for folks who bought it previouslymeaning legitimate owners of the software can no longer re-download it. (Some Macworld staffers actually do see Lion in their Purchases tab, but ironically enough, that seems to be limited to those who didn't actually purchase Lion, but rather acquired it through redemption codes from Apple)

That means that folks who own Lion and, for whatever reason, want to install it fresh on a compatible Mac, can no longer do so. Cautious Mac users who try to remain one major Mac OS iteration behind the current release are out of luck now, too. It looks like Apple will offer just one version of its desktop operating system in the Mac App Store, and that version is Mountain Lion.

As a reminder, before you install Mountain Lion, it's a good idea to make a copy of the installer. Otherwise, the installer gets removed from your system when the installation process completes. To make a copy, Control-click (right-click) on the Install Mountain Lion icon in the Dock, and choose Options -> Show in Finder. With the installer selected in the Finder, choose File -> Duplicate. Then continue on with your installation process.

Apple hasn't yet responded to Macworld's request for comment about Lion's disappearing act.