Ludi, I am new to this topic and haven't been pondering the implications of PO for years, as Monte has... So my reaction is that of a beginner. I would only defend the first post, as they are my only thought out and truely planned postings. That is...
1)doomers tend to accept the worst regarding timeframe (earliest PO date, fastest rate of fall in production 9%/year) while holding to the belief that there is zero time or ability to adjust infrastructure and use. If events are further off or more gradual than that, and our reaction is less paralysed by war, disease and economic collapse then there would be a possibility of reacting and adjusting transportation.
2) Doomers are also more likely to see the dollar as a house of cards, set to collapse under stress. I'm no economist, but am just pointing out that this is a view not commonly held. If you search for topics on the US dollar collapse or petro-dollars you get peak oil and conspiracy sites. I would think that if it were not somewhat fringe it would show up on more mainstream topic boards. It's arguable (not very well by me, but possibly by others...
http://www.peakoil.com/fortopic3761-450.html ). And, it's one more level of complexity to the problem. Is it intellect and insight that causes doomers to see, accept and discuss a collapse that the world isn't discussing, or is it pessimism?
3) They lump the peaking of oil, gas, coal and nuclear into one immediate innevitable catastrophe. I've seen this done on many posts... In fact peak coal is some few generations off and peak nuclear is beyond discussion thanks to thorium and breeder technologies. Is this pessimism or wishful thinking (belief that the system should fail now anyway for other reasons, so no reason to wait)?
4) They underestimate the impact demand destruction (decreased use) will have on prices... We just saw increasing prices decrease US demand this fall... Resulting in decreased prices. The interaction between increasing prices and decreasing demand is another layer of complexity making pricing predictions impossible. As demand destruction plays out over the globe where will prices settle. ?Sky high? Monte thinks so. Can the indian, asian, south american or south african driver really pay 7 dollar/gallon gas? If not, then Western consumers will get gas for less than 7$/gallon. I'm just raising questions here. Assuming "sky high" assumes someone can pay that price for the volume that OPEC nations need to sell... I'm just raising question.
5) They (correctly) point out that there will be no single replacement as plentiful and cheap as oil... but imply that that means that a patchwork of more expensive, less energy dense solutions coupled with conservation (driven by economic necessity) can not be successful. By successful I mean survival in a industrial-ish society with electricity.
6) They discount technology's potential impact on energy availability and storage... Bah Humbug is the response, if I remember correctly. Lithium nanotechnology discovered this year is resulting in a powerful new fast charging generation of electric drills next year. An optimist would see that scaled up to electric vehicles soon (as the company websites suggest). A pessimist doesn't leave time on the horizon for innovation, or starts worrying about peak lithium. It's just a trend I've noted.
7) They too easily accept the notion that the US economy/industry is without value and that the US dollar will fall to zero value easily. Actually this is the same as #2.

They use arguements based on efficiency and EROI to discount viable projects... Bah Humbug is the response, if I remember correctly.
9) Let me ad that Doomers are more likely to believe that there is a segment of elites steering us toward this chaos, looking foreward to it, and planning to put us in labor camps in a few years guarded by blackwater security. I'm not going to try to disprove this (if it's true we are in trouble) but just mention it to point out that doomerism is more than a conclusion, it's a way of life : )
Anyway, that's the most I will defend. General observations. That and the observation that as each point (depletion, political, economic, technological) has uncertain timing and outcomes when combined the uncertainty multiplies. You can decrease the variability of your predicted outcomes by always choosing the worst case scenario (doom x doom = doom squared) but that may not increase the accuracy of your prediction.
The rest was just rambling... As I find the initial steps and years too complicated to accurately predict anything compounding initial guessis is nothing more than conjecture.
PS- Looking at humans as a population in a limited environment is the most compelling and undeniable thing about the doomer arguement... Still the carrying capacity of the earth under future conditions (and what those conditions will be) is not yet certain.
PPS- What this thread has really taught me is how indefensible it is to have enough to eat in the US while not attempting to help out the poor places on the planet... Starvation is really easily preventable, and is probably man's most primordial fear. Food and birth control is a basic human need.
PPPS- Again, it is funny that I would be put in the role of defending an optimist viewpoint... Pessimism and fatality come to me much more easily than optimism.
PPPPS- Looking at humans as a population living beyond it's means on a small planet is the strongest argument for doomerism... But predicting the timing of our demise is difficult.