1) Well, I just sold mine. I liked the simplicity and the fact that it did add a "little" something, but I didn't like the fact that it was hard to distort (and I didn't really care for the distortion). It has three essentials in one pedal - LPF, HPF, sweepable mids. However, if I were to look for something similar in the future i'd either go with an RFE or Messenger, both much cheaper and readily available. Most ppl that try the S1 and the Messenger don't hear that much of a difference (if at all) and i prefer the OD on the Messenger.
2) Like @el murdoque said, it's vintage tone all the way. Thick, juicy, sweet, powerful vintage tone to be sure, but it won't sound modern. Definitely one of the best vintage pre's out there though.And I LOVE me a Fender tone stack. I'm a huge fan, and it's one of the preamps that made the cut for me and I plan on keeping around.
3) It's getting further up on my list to try!