Perhaps you've read this... http://www.peterwhitecycles.com/fitting.htm
If not, it's a worthwhile article if only to give you a baseline for making adjustments.
This is also a good reference article, although somewhat more heavy on the technical side of things:
In general, seat height, seat tilt and the reach to your handlebars should be established based on a "best fit" relative to your body size.
As you ride on different terrain you do as GeorgeSnatcher suggests with regard to power...
Climbing: You slide your butt further back on the saddle -- behind the neutral postion and further back of the bottom bracket -- to bring your quadriceps more into play.
Fast, flats: You slide your butt forward on the saddle -- in front of the neutral position and above the bottom bracket -- to leverage your hamstrings.
Regarding seats, the foundation materials used in most modern saddles will tend to break down if they were somewhat thick to begin with. In a word, thick padding on saddles is a "bad" thing. The older they get the worse they are as they let and more weight move onto the soft tissues where nerves and blood vessels can end up being restricted leading to all kinds of discomfort. A firm saddle is a good thing.
Anotomic cut-outs are also not necessarily bad things if they are part of a firm saddle for a variety of reasons but they're not for everyone. I've found that I like them relative to pressure relief on the "tweeners" and for the free air conditioning. It's amazing how much cooler a cut-out saddle is on a hot day vs a solid model.
Can't say much about the gel saddles. I've got some on my single bikes w/out the anotomic cut-out and my biggest issue is they're too soft and the coverings seem to wear out fairly fast.