It ought to be a simple quesiton, and in part ?i can answer it for myself: I have the same saddle on both my road bikes and one of the MTBs (the other is a shonky singlespeed that doesn't warrant any more money to be spent on it).
However, I've noticed that a number of guys I ride with seem to have different saddles on different bikes.
I am (I hope) going to buy a mate's old track bike (for use on the track - I'm too old to be a fixie kid with an asymetric haircut and my kid sister's jeans). Quesiton is, the geometry is necessarily different from my road bikes with a much lower front end, and I fear I'm not going to like my usual saddle choice on it.
Am I just being ridiculous?