i've seen this thing around but what the heck does it do? anybody have good soundclips?
a feedback looper is an effect into which you connect all your other effects and, when engaged, manipulates the sounds to make chaotic, otherworldly noises. check out death by audio's website for samples of their "total sonic annihilation" feedback looper.
it causes your pedals to feedback into themselves, how it sounds exactly depends on what pedal(s) you run through it. But it usually makes some pretty bizzare noises.