Would You Use It: Mogrify Helper
Mogrify is a command-line interface to the imagemagick libraries. It's capable of some pretty impressive voodoo when it comes to performing batch operations on images, which is something that comes up from time to time.
Unfortunately for you, the user, mogrify's syntax is a bit tricky. Straight resizing is easy enough, but add more than a few options and things become unmanageable. Plus, a few of the defaults for things like resizing could probably give better results with some more advanced parameters. I don't know what these are yet, that would take some research.
My idea is an interface that lets you line up and individually configure a bunch of operations to perform on your set of images, and spit out the necessary command to do so. I originally thought of having the user upload images, have them mogrified, and then download the new images, but that seems unnecessarily tough on bandwidth, especially when you consider that mogrify is most useful for batch images.
Future extension could see it automagically creating commands for Apple's SIPS and other comparable software as well.
I'dve certainly found it useful to have something like this a few times in my life. But I'm not sure if that's true of anyone. If you are reading this: would you use it?