Subject: gravity and centripital force of a rotating planet

I've already read 855511961.Ph and it answered my basic question,
which was why the gravitational accelaration ('g') of a planet could
be determined solely by its mass.  The answer implies that the 
ellipsoid shape of Earth compensates for this effect, but this
explanation leaves something to be desired in my mind.  Consider 
the following questions:

- Is it true that if a perfect sphere were not rotating, the force
on a body on its surface ('gravity' felt) would be _more_ than that of
a planet that was rotating (due to centripital force)?  And that this
lessening of "gravity" would be maximal at the equator and nonexistant
at the poles?

- If above is true, then why are gravitational accelarations
calculated on mass alone (or am I mistaken)?

- If centripital force acts in the opposite direction as gravity
(as would seem to be the case based on one's "natural sense") then 
why does the ellipsoid shape of the Earth explain a consistant value
of 'g', since the Earth has its largest diameter at the equator?  
Shouldn't the Earth have to have its smallest diameter at the equator, 
so that the force of gravity would be stronger to compensate for
the effect of "things on the surface of a spinning object wanting
to fly off"?

- Finally, I realise that "centripital" force is the force exerted 
ON a body to keep it in orbit, and this force is directed inwards
and does no actual work on the body since it's always perpendicular
to the direction of motion, but then what is "centrifugal" force? 
Its name would imply the force "coming out away from the center", 
or in other words the force most commonly associated with a spinning
object, i.e. "when you spin something, things attached to it seem to
want to fly off."

Thank you for clearing up these uncertainties that have always haunted
an otherwise lucent view of classical physics.

Re: gravity and centripital force of a rotating planet