Join Date: Jun 2004
Location: Northern Nevada
Grant Petersen at Rivendell recommends Obenauf's Leather Preservative, which you can get at many boot places. I've used both and can't tell a difference (one of my B-17s is ~20 years old). But as Scott said, it just keeps the leather from drying. You don't actually want to soften it anyway--it shortens the life.
Some other tips that have worked for me:
I've found the break-in horror stories to be exaggerated. I have three B-17s, and while they do get better in a few hundred miles, all were comfortable right out of the box. Just ride.
Setup is critical, at least for me. A couple of millimeters up or down on the nose makes a big difference. Use a ruler and measure from the top tube.
Whatever you smear on, use it sparingly. I think Grant says a gob the size of a pea once a year. I live in the desert and do it twice a year. It took me six years to use up a can of Proofide, even with four saddles (I also have a Pro).
Protect it from water, and if you get it wet, don't ride it until it dries. I keep a plastic grocery sack in my seat bag in case of rain. I should probably protect it from sweat, too, but I can't bring myself to do it.