Based on http://ycombinator.com/howtoapply.html, it seems that there's a point in the application where if you're impressive enough, they'll spend more time on it and if not, they'll disregard it.

> If the founders seem promising, I'll now spend more time trying to understand the idea.

It might be a good idea to put the applications that don't get past that point in one pile, and send them a different and more specific rejection letter. (I was just rejected and am naturally wondering how close I was, and this idea came to mind.)