It's one of the toys that every guitarist tries at some point. I think my first experience was part of a cheap multi-fx unit, maybe a Korg Toneworks, maybe ten years ago. Being fairly new to playing guitar, and playing a Squier with really nasty sounding singe coil pickups, it all sounded rubbish. I started playing my bass in a 3-piece grunge band not long after, and needed a really huge sound. My long suffering Fender BXR 300 was plenty loud enough but had a really clean sound, so in came a Sovtek Big Muff and a reasonably priced copy of a Cry Baby. It really made the sound of the bass jump out, especially for random showing off.

Of course I went my own way on effects and started getting into rack stuff that I couldn't break as easily, and when the Big Muff and the Wah broke I didn't think much about replacing them. But I sometimes found use for the expression pedals on my midi floor controller, first for guitar effects manipulation and when i got into synths, for controlling, well, just about everything. For my own amusement I'll tweak the Q (resonance) and the frequency (Cutoff) of the resonant filters. These are more often a low pass rather than a Wah style peak filter, and often resonant to the point to self-oscillation, but I didn't really consider their connection withthe humble wah and how my use of filters has gone full circle.

Anyhow, BoingBoing has the documentary