One thing that respondants to the synthetic oil debate have not
addressed is viscosity under different temperatures. While conventional
engine and gear oils turn into a thick sludge when cold, synthetic oils
remain much the same as when at normal temperatures.

During construction of the Alaska pipeline, trucks used to be left
running 24 hours a day because they were too hard to start when the
engine became cold. Synthetic oils were later used, and the trucks were
found to start more easily. Leaving them running all the time was no
longer necessary. A good demonstration of principal is to install
synthetic gear oil in a manual trans. You can actually feel the
difference in cold shift pressure yourself, unlike engine friction. I
used to have a hard shift problem when cold that was cured adequately 
by shifting to synthetic gear oil (not VW, but worked in both Alfa and
Mitsubishi trans). 

Synthetic engine oils may under cold conditions be pumped up to
operating pressure more quickly than conventional oils saving engine
wear, regardless of what consumer reports says ..... I can't forget that
my parents bought a 1959 Rambler based on their recommendations. Taxi
cab engine wear is probably more a function of driver abuse than
lubricant properties.

And as food for thought, in a long-term experiment, my 1984 Mitsubishi
truck which was run exclusively on synthetic oils and changed at 3K
intervals has 140 PSI compression at 160,000 miles, the spec for a brand
new engine (and no, it is not due to carbon in the combustion chamber!).

DDF
(Former chairman of Society of Automotive Engineers in San Diego)