Is hydrogen a realistic fuel of the future (when the oil runs out)
when it takes more energy to produce it then the hydrogen yields
itself?

It would be a lot more productive and cost effective to use battery
instead of Hydrogen fuel powered vehicles. But, filling up is a lot
more profitable, so the petroleum industry would be more interested in
developing this technology (hydrogen) despite of the dangers involved
than investing in developing the efficiency of batteries.

There is a pretty good movie/documentary about it 'Who killed the electric car'
www.whokilledtheelectriccar.com/

Hydrogen is currently a bit dangerous to transport
- they currently have fuel cells that work on it
- what would be useful would be finding a stable way of transporting
it in liquid form
- about 20 years ago I heard of some 'earth' that absorbed hydrogen
with a weight to power ratio similar to that of petrol.

I reckon that there is quite a lot of scope for producing hydrogen
from eletricity generated from tidal power. It is simple clean
technology and does not need to be particularly efficient.

Personally If I were running an oil major, I would be looking at
building two tier tidal dams - for electricity and derived products.

You're right that Hydrogen currently takes more energy to produce than
it provides.  That is a very losing battle.  But if we don't try
hydrogen to see how it goes, no one will have incentive to make
hydrogen technology better.

Ideally, hydrogen technology will advance far enough in the future so
that it becomes a positive energy flow.

Firstly, oil will not necessarily run-out; it is more likely that it
will be superseeded. If you think about it when oil supplies fall
short the price will go up and up and other technologies will become
cheaper (relative) to oil. Another possibility is that oil will stay
cheap but a new technology will be so good and so cheap that it will
replace oil. Either way oil will be more expensive than the new
technology and consequently there will be no need to drill it. (There
is a famous quote which is something like "the stone age did not end
because they ran out  of stones and the oil age will not end because
we run out of oil")

With regards to hydrogen energy, it all depends on technology and if I
could predict  the technology of the future I will not be attempting
to answer this for a mere 20 bucks! My comments so far have not been
very helpful so I will now try and write something which kind of
answers the question. There is no doubt that there will be a
technology in the future that replaces oil. It is impossible to
predict which technology will win the battle and when oil will be
replaced, it could be hydrogen although it could be electric cars or
bio-fuel cars or something completely new - who knows? I think that
the forthcoming "technology war" is similar to what happened a 100
years ago. Then no-one knew how cars would be powered. Believe it or
not but at one time 30% of US cars were electric and steam cars were
marketed too! But the oil combustion engine won the war. In a few
years there will be a similar competition between competing
technologies and consumers will  choose the best technology.

With reagrds to hydrogen proper I can see no reason to rule it out,
despite the inefficency of process. What matters is not the effiency 
but the cost (and other considerations like carbon might be factored
in through government regulations and taxes). However, I have been
concentrating on cars for good reason. The inefficency of the process
does rule it out for electricity production (why produce electricity
from hydrogen if it takes more electricity to produce the hydrogen in
the first place?) but it does not rule it out for automobiles. This is
because other factors like how long the hydrogen fuel cell lasts will
be important. For example, suppose that an electric car needs
recharging every 100miles but a hydrogen car needs topping-up every
500 miles. Even though it takes a load of electricity to get the
hydrogen people would prefer the hydrogen car to the electric because
they don't want to constantly stop and charge-up their car.

Therefore hydrogen might be the fuel of the future for cars, but it
can only be the fuel for electricity if we find a much more efficient
way of getting the hydrogen.

Hydrogen is not a fuel. It is an energy storage medium. A battery. A
very expensive battery.

Eestudent:
"Fuel is material with one type of energy which can be transformed
into another usable energy. A common example is potential energy being
converted into kinetic energy, (as heat and mechanical work). In many
cases this is just something that will burn."
en.wikipedia.org/wiki/Fuel
"a substance that can be consumed to produce energy"

://www.google.com/search?hl=en&lr=&defl=en&q=define:fuel&sa=X&oi=glossary_definition&ct=title

Is the hydrogen not consumed to produce energy?  I'm not flat out
disagreeing with you because I don't know much of anything about fuel,
I'm curious from your post if I simply don't understand how the
hydrogen is used.

I believe his comment is a reference to the fact that breaking up
water to get Hydrogen takes more energy than the Hydrogen will
produce. So it could be thought of as a medium to store the energy you
used to break it up physically take that energy to another location
then put it to use. Much like charging a battery would be.

There are a few advantages to hydrogen power.  Those folks who refer
to hydrogen as a "battery" are essentially correct: it's just a device
to store energy.  It has a few advantages:

Hydrogen is fairly lightweight
It stores a fairly large amount of energy for its weight 
It can run a fuel cell, piston-type motor, or turbine
It burns very cleanly, producing only water as a byproduct
It's easy to produce by several means: if you have a cheap source of
electricity you can make it out of seawater.  The tidal idea has
promise!

Another thing: hydrogen can be made at the source of the electricity,
stored indefinitely without any loss, and transported to wherever it
is needed.

You could "fill up" with hydrogen very quickly, whereas with batteries
you would either have to wait a bit for them to charge, or have some
sort of exchange system, where you'd leave your battery pack and
replace it with another fully charged one.

Batteries have a few disadvantages, especially in cars
They aren't very efficient. I don't know what the efficiency is for
hydrogen production, but the best a lead acid battery can do is about
15%-20%.  Thus if you use 1000 watts for an hour to charge a battery,
you'll only be able to get 150 to 200 watts for an hour out of it! (or
you could get 1000 watts or so for about 10 minutes: you get the idea!
You lose 80%-85% of the power you put in!)

Some of the newer batteries (non lead acid) have better efficiency,
but the very best still only get 30% or so.

Batteries are heavy, expensive to buy, and generally last about 5
years. If you buy a hybrid you can purchase an extended battery
warranty for 10 years, but they charge $2000 for the warrranty! (I
think the battery pack is over $5000)

There are other energy storage devices in the works, so it is hard to
say what we will end up with in the future.  Batteries may become more
efficient and cheaper.  Capacitors are getting bigger and bigger, and
they are quite efficient: many VCR's use a 2 farad capacitor instead
of a battery for backup!
They used to say a 1 farad capacitor would be the size of a boxcar:
these 2 farad ones are about 2 inches in diameter and a half an inch
thick!

One thing that will become interesting with electric and other
alternative fuel cars as they become more popular: who's going to pay
for the roads?

The local state and federal government tax gas and diesel quite
heavily to pay for the roads.  An electric car owner wouldn't be
paying that.  If electric vehicles become more popular, expect some
sort of yearly tax or somesuch to be enacted.  Of course any "fill-up"
scheme like hydrogen or ethanol would use the existing tax strategy.

Speaking of alcohol: it might be the fuel of the future! It can be
produced biologically: I could see  genetically engineered bacteria,
plankton, or whatever sitting in the sun making alcohol all day out of
sunlight and grass clippings!