Ok, so if we first assume that the nose is NOT tipped down too much- you have it tipped up enough to keep you from sliding forward, right?
With that assumption...we can move to the question of saddle forward or back.
If you feel you need to scoot back on your saddle frequently, is it perhaps because it makes you feel better balanced weight-wise over your center of gravity?
With the seat forward, your center of gravity is shifted forward as well, more over your pedals, and the extreme would produce a feeling of falling forward onto your hands.
Moving the seat BACK will shift your weight and center of gravity back more, behind your crank and pedals. It can give you more pedaling power, but the extreme would produce a less upright back and perhaps a reach problem to the hoods, etc.
...Just my humble opinions.
Here's a good general article about saddles by Sheldon Brown:
http://sheldonbrown.com/saddles.html
And here's a good article about saddle positions by Peter White:
http://www.peterwhitecycles.com/fitting.htm
Both Sheldom and Peter are highly respected bike guys. :cool:

