Our very own Tremeloking does a Boss DS1 mod. I just got mine about a week ago and would like to present a review here.
Firstly, Ron is a heck of a great guy to work with and he really knows his stuff. But you probably already guessed that from his posts on TFF.
I bought a brand new, modded DS1 directly from him (at a very reasonable price). I did not previously own a stock DS1. Nor have I ever owned or heard (other than online clips) various other modded DS1s (Keeley, analogman) So, this is just a review of the pedal on its own merits.
My gear: Fender Tele with Kinman p'ups into a SFDR. I also use a Fulldrive 2 and a Crybaby. That's about it right now. I was looking for something to pick up where the FD2 left off and give me some true distortion. My band plays all original comedic rock and sometimes we need to spoof hard rock/metal type stuff. A Tele and Deluxe Reverb really isn't the thing for that but the DS1 got me in the ballpark.
Ron's DS1 has got gobs of thick, lucious distortion in there. The tone control is extremely useful as well and it seems to interact nicely with the distortion control. I can dial in some warm, mellow stuff, edgy crunch, or singing violin leads. My amp is voiced with a mid heavy A channel so when I switch to that side it sounds like a TS9 on steroids.
I bought it for the heavier distortion type stuff but the pedal also sounds very good rolled back a bit. It seems to cover overdrive territory very well.
I've had other distortion stompboxes before and they seemed to be plagued by a nasty buzzing tone as you dial in more drive. This one isn't. The sound coming through is very pure. It still sounds like my Telecaster, only much nastier. The guitar shines through.
Get yourself one.