On a Mac there's a feature called Quick Look, it shows you an enlarged picture of the application, and some information about it.
QuickLook also works great for files. I can't really see QuickLook being used for apps, sorry I just don't see it. For documents, yes, or even a lockscreen information "tab."
To show use of apps in Quick Look, and a demo for those who aren't familiar, here is a couple of images of quick look:
After selecting a file and pressing the spacebar, you will get a window like this:
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Applications will give you name, version number, copyright info, and size:
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Folders will give you name, size, and number of items:
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Documents will give you a graphical preview of the document:
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And images will give you a preview, and an option to open in iPhoto:
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(note the iPhoto icon at the bottom)
After seeing mickbab's post, I think it will be used to preview what apps may be contained in folders on the home screen.
Keep in mind that the features that are shown in the picture are for developers to implement into their applications, NOT features in the new OS.