Well, I got the pedal back on Wednesday, and spent a couple days playing around with knobs. This pedal is a totally different animal than it was when I bought it. Before, it was a decent distortion box, but it was VERY sensitive to knob placement. There were only a few settings you could dial up that weren't overly fizzy, thin, and brittle. No longer.
The other reviews I have read of John's DS-1 mod are spot on, it sounds like a pissed-off Marshall. The first thing I did was put it in front of a clean channel on my Mesa Rectoverb head, with the volume set to a slight boost, tone around 1 o'clock, and I just played with the gain. You can dial in anything from a slightly raunchy gain a la AC/DC or ZZ Top, on into some pretty hefty gain. You could probably do some classic metal tunes quite easily. The pedal cleans up nicely with the volume control, though you'll never quite get all the grit out with the big balls John implanted into this pedal.
I was overjoyed when I ran the pedal into the drive channel on my amp. I had to keep the gain around 9 o'clock though, and just use it as a boost to avoid a swirling mass of feedback . The pedal really thickened up the tone, and gave it a different attitude. Gobs of gain on tap here, but didn't get too muddy or fart out, and it didn't ruin the dynamics of my playing.