Dmitri Orlov has written an excellent article here, which I'd recommend reading, the gist of which is that the 'descent' of oil production will be much steeper than the standard Peak Oil analysis expects. I have no dispute with his analysis, so far as it goes. I agree that reserves are overstated (and we have front-loaded the extraction); that the Export-Land problem is very serious; that EROEI will exponentially reduce the available of energy as such oil as is extracted; and that there will be systemic break-downs of the infrastructure needed to extract oil. All of which makes me think that, taken together, we (average Westerners) are looking at severe oil scarcity within about ten years (possibly sooner) and that, if we haven't as a society shifted away from oil-dependency, then our future is solitary, poor, nasty, brutish and short.
So why do I think his pessimism is overdone? Two principal reasons, one specific, one (flowing from the first) more abstract.
The specific reason why I believe the pessimism is overdone is that our culture is massively wasteful of energy. Take transportation: most cars in most morning commutes carry a single occupant, when they were designed to take four. Setting up car-sharing agreements is technologically straightforward and would have all sorts of wider social benefits in addition to the reduction in petrol consumption. In other words, this is an 'easy win' - and it is an easy win that can be adopted rapidly, which means that it buys time to deal with the more fundamental issues, which is the most crucial point. There are other easy wins (like home insulation, CHP) along with some other not-so-easy-but-very-likely-to-happen 'wins' like: we'll be colder in the winter and have to wear more jumpers rather than turning up the thermostat. My 'wild-assed-guess' is that we (the UK) could face a 50% reduction in the availability of oil and just about keep the show on the road - not without a great deal of hardship, and not without having to rely on a very great deal of social solidarity and rationing etc - but I think we could do it.
Now this is just a temporary fix - it will give us, I would guess, ten to fifteen years of time 'coping' with Peak Oil - which leads to my more abstract grounds for optimism, which is that the Western way of life is dynamic, not static. The greatest problems facing our civilisation are not technical, they are social, political and spiritual, and the biggest problem of all is a refusal to face up to the reality of our predicament. If my first point is anywhere near true, then the one certain thing that will flow from it is that people will realise the nature of our crisis and, in typical human fashion, respond rapidly and adaptably. When motivated, we are able to do all sorts of ingenious things, the best example of which is probably the retooling of our factories in order to fight WW2.
To my mind, the issue is not whether the world as we know it is coming to an end (it is, we will see [DV] the end of a society based around the assumption of perpetual economic growth), nor whether civilisation of some sort will continue on afterwards (I have no doubt that it will). What I ponder is what sort of civilisation will there be to succeed our present one, what values and achievements will we be able to salvage from the wreck of Modern Industrial Civilisation? I am optimistic that we will be able to save a lot - but that is undoubtedly a moot point.