"After years of admiring everyone else, I sprung for a Brooks B17 saddle last week. Right now it is a b---h - I find I keep sliding forward on the smooth leather and driving the wedge into my perineum, so I'm pushing against the handlebar to keep my sits bones on the right spot. I hear that over time the leather will soften and shape to my sits bones - won't be a moment too soon when that finally happens."

Your saddle is tipped too far forward and this is what is causing the slippage... set it level or with the nose up just a little and you will notice an incredible difference in comfort.