First of all, this has nothing to do with CS3 or CS4. It has nothing to do with Adobe. It's Apple's implementation of their OS. By default, Illustrator embeds PDF versions of your file in each document, if you save it with PDF Compatibility turned on. Apple's OS can read and display PDF files, but for performance reasons, the OS only does this for files under a certain size. Anything above that size is displayed the document icon.
With Tiger, Apple started to implement a feature called QuickLook that allowed you to better preview files directly in the Finder and really anywhere the OS is called (Open and Save dialogs, etc). This feature got better in Leopard, and Apple also opened this feature as an API so that other developers could develop custom readers to give extended functionality to the QuickLook feature.
Code-Line software developed such a plugin that enables Apple's QuickLook feature to display Illustrator files, even if those files saved with PDF compatibility. In this way, you can simply tap the spacebar in your finder with any AI file selected, and you'll see a preview, PLUS a list of some of the metadata for that file (fonts used, colors used, images used, etc). The SneakPeek plugin works not just for Illustrator files, but also for EPS, FreeHand, and InDesign files. It's a valuable plugin, in my opinion, and the cost is $20, not $50.
:) Mordy
