for sifting through <50 or so files, it can be nice/useful. For sifting through >1000s of files, it is a huge waste of time. Besides, with quick look, it is so much better to just quickly find your file via the list view, where you can actually organize by preference, and then simply 3 finger tap (on a trackpad) to quick view, giving you a much bigger window to see the file anyway.
It was that kind of feature that looks nice and you like at first, but then you find it to be completely unproductive. However, I have to say that I don't like the replacements introduced in iTunes 11 and iOS 7 neither (both will be crap until they get some sort of alphabet list on the side/bottom).