I believe the answer is: 'it depends'...

There is a third path for the same money- use a high quality conventional
oil and change it twice as often as synthetic.

Not that you could measure.

Absolutely not.

Follow the manufacturer's recommendations for frequency of oil changes and
stick to the viscosity and grade of oil the manual recommends for the
temperatures and the conditions that you drive under.

More frequent changes are not bad, but they aren't necessary for long engine
life.

Check what the manual says are conditons that qualify for 'severe service'.
Chances are at some times your typical usage will fall into that category for
one or more reasons.  Severe service intervals are much shorter than the
standard service interval.

The one thing that would make me use synthetic is needing to start the engine
in extreme cold conditions without a block heater.

I would certainly use a good oil rather than a cheap oil. Synthetic is
best suited to high performance engines or if you are constantly running
your engine at or near the limit. For your average type of everyday
driving, a "good quality" mineral oil will do.

If you are using the car for a lot of short journeys where the engine
doesn't always warm up properly, you should consider changing the oil
more frequently than recommended by Ford. My average journey is 35 miles
and I still change my oil every 6,000 miles. This may or may not be
overcautious but I intend keeping the car for a long time and if I do
have problems with the engine, it won't be for the lack of maintenance.
The extra oil and filter change only cost me about £20/year so it's not
a big deal for me.

Personnally I'd rather change the oil at half the recommended interval, and
use a good quality SH or SJ rated mineral oil of the right viscoity (5w-30
for most fords now) rather than use a synthetic costing probably more than
twice that of the mineral oil yet not being upto the job of going twice the
distance.

I change it at 5k / ~5month intervals in my Focus, which is at a point where
its just turned dark brown and smells of "combustion" residue.

If you want an engine to do a big mileage, there is just no substitute for
regular fresh clean oil.

Tim..

There are only two conditions under which synthetic oil provides an
advantage

a) very cold weather, where synthetic remains more fluid and allows easier
starting (useful here in Ontario)

b) very severe hot conditions, such as racetracks in Arizona in July.

Other than that, synthetic is just a waste of money. Some brands do
advertise longer change intervals, but to me that's a crock. Synthetic oil
may last longer than regular oil, but it gets dirty just as fast.

The point is, that if you change oil sensibly, your car will probably go to
the crusher before the engine wears out. So any technical advantage of
synthetic is irrelevant.

I disagree with most all of you.  Syn oil does give better mileage, does
last longer, and produces less wear on engine parts.  Research it yourself.
At work I have a good url I will post tomorrow for all to look at.  And as
for oil being cheap or expense depending where you live it is not a
renewable resource.  Waste it now and your kids might not have any.  I say
use it to the max.  At least as long as the manufacture recommends.

Good comments about longer interval in some countries than other countries.

Had One

Here is the link

http://neptune.spacebears.com/cars/stories/oil-life.html

Had one

James,
I can relate some experience with the subject of your question, and have
asked myself the same question in the past. At one point in my life I was
driving 70K+ miles a year. At that time, I was using parafine (regular oil)
based lubricant. I would change oil and filters every 3,000 miles.
Invarialbly after 100K miles, I would experience some increase in oil
consumption. Not unusual or anything to worry about with a 100K+ engine.
Worn valve guides alone could account for some increase. What I did notice
however via the tailpipe was an increase in oil residue, a clear indication
that some oil was getting past the rings. About ten years ago, I replaced
the head gaskets on a Ford 3.8L six that had blown the gasket on the right
bank. This particular engine was notorious for losing head gaskets. In
visiting the shop doing the work, I was dismayed by the amount of crud that
had accumalated in the valve cover gaskets, and around the lifters. My
mechanic suggested that I switch to synthetic (Mobil 1) to elimiinate the
problem. He also explained to me that most wear on any engine takes place it
the first 15 seconds after start up. That's usually the amount of time
required for your oil to be pumped through all the journals and get to the
top of your engine in full operational quantity. Until then, your internal
parts are reciprocating with minimal lubrication that was left from your oil
residue the last time you shut off your engine. This is where synthetic
becomes important. The residue of synthetic has far superior lubrication and
viscosity properties than regular oil, allowing more protection until the
pump brings more to the top of the engine. Second, synthetic maintains
viscous properties at far lower temperatures than any petroleum based oil
and will be pumped to the top of the engine and flow through those journals
much quicker. Third, synthetic maintains protective lubrication properties
at far higher temperatures than regular oil, and will not leave deposits
(crud) on the top side of your engine when heated to extremes. Since the day
my mechanic talked me into synthetic, I have used nothing else, and have
taken three vehicles well over 200K miles with not one internal failure,
including timing chains, no loss in compression, nor any increase in oil
consumption. One note of caution. I would not use synthetic in a brand new
engine. Reason? Even with todays CNC close tolerances, there is still a
"seating" period every engine must go through. Synthetic oil offers such
high levels of lubrication, that this "seating" may take much longer (if
ever) and I would recommend you wait until the vehicle has somewhere around
12K miles. Oh, by the way, I change oil and filter every 6,000 now instead
of every 3,000. I know the synthetic manufacturers say you can go much
longer, but oil life is not the issue, dirt is. No matter how good the oil,
you are still going to suck a certain amount of dirt past your filter and
into the engine. I figure by doubling my time interval to 6,000 miles I am
paying nearly the same as regular oil every 3,000, and enjoying the benefit
of far superior protection at the same time. Good luck.