I've been working on a little app that lets me download large files from my Dropbox account using Adobe Air. Essentially, I needed a way to download 700+ MB files without them going entirely into memory first (I want this app to run on any device). So that rules out URLLoader.
Basically, I needed a way of progressively downloading the file, and offloading it onto the hard disk to clear up memory for the next bytes of the download.
Here's the Download class (keep in mind it only works in Adobe Air). You can also download the class if you like.
Thanks to Stackoverflow user Pascal for his insight and writing the Stackoverflow answer off of which I loosely based mine.