Just My Imagination

Downloads show up in a toolbar at the bottom of the screen. When you click on one that hasn't finished downloading, it tells you "opening in 3 minutes" (or whenever the download is estimated to complete).

I don't know if you've ever tried to use a computer that was processing too much at once and had a delayed reaction to clicks and other events. It would be amazing for the interface to show that a particular click was waiting to be processed. It wouldn't have to do any extra processing to calculate the delay or anything, just acknowledge that it received a click in that spot with a little starburst or something. Not the candy, the shape! :)

There's also a subtle emotional impact to your computer telling you it can't do something right away but it will soon...and then following through.