I wanted a delay effect, but one that takes as little space as possible in my Ukulele bag. You'd think some kind of minimal plug-in effects existed, but I didn't find much, so I compromised by buying a cheap delay, the VD-400 from Behringer, and making a smaller housing for it. I had to remove the pedal to make the box smaller, but for my purposes, that's fine. It's still nowhere near as small as I'd like, but the PCB was pretty big to begin with.
I think next I'll look into some kind of more software-oriented solution for effects... Maybe a Beagleboard or something could be used to run basic audio processing. Pedals seem to be made the way they are simply because they need to be pedals, there has to be a way to make an effect processor smaller.