PEKIYASIMDI  It is not good for me. When you look a document (whatever it is: eps, fh, indd or ai), it does what it is expected. But when you want to look another document it shows inside of the first document you look. :(  
(Version 1.2.1)

BEIGE  Stop whining about the price - this thing is actually quite useful and worth it for my magazine. I can see what spot plates and fonts are in our Indesign files with a full preview - in the desktop.  
(Version 1.1)

STORMCHILD  I wouldn't say that the work that went into this isn't worth $20, but it's pretty annoying that QuickLook doesn't support .ai files without a plugin, since the entire OS X display system is PDF-based.

A better solution, going forward, would be to save Illustrator documents in "Illustrator PDF" format, which should display in QuickLook with no plugin.

They did do a decent job on the plugin, but I'm really not looking for lists of colors used in the document and things like that -- I just want QuickLook to display .ai files the same way as any other image file format (other than gradient meshes, which are apparently never going to display correctly in non-Adobe software -- unless those are part of the PDF standard that Adobe just submitted to the ISO).

The clincher is that this plugin does not understand layer visibility, so all the layers I have turned off show up in the preview. This makes it borderline useless.  
(Version 1.1)

GCOGHILL  It might be $20, but it not only does what it says, it has a lot of great features beyond just a preview.

$10 and I would have already bought it, but I find more and more that it would be really handy after demoing this and might bite the bullet anyways.  
(Version 1.1)

LOWFI  A 20 dollar quicklook plugin???  
(Version 1.0)