The effect that peak oil has will depend on people's (read societiey's) responce to it (wow big surprize i hear you say!).
Whether there is a slow decline in oil use and a general addaption to a low energy society by the mundanes (Such as is happening in the transition town movement in the UK), or a technological maximisation that results in a steep decline or "crash" is one of the major factors.
In the event of a crash there will be no way for those who have 'converted' if you like to support those who continued to live in a centralised and unsustainable way.
If governments continue to subsidise crops to make bio-fules and such like - technological pipe dreams that people can cling to then the FF energy that the world has left will be squandered instead of being invested in a realatively sustianble future.
the USA, and indeed most western countrys, all big cities and most larger towns would fall appart and people would die if the oil dropped off too steeply.
It is used in the manufacutre of commercial pestacides and fertalisers and many other chemicals, to say nothing of the numerous oil based plastics that ssociety is addicted to.
Oil is key in the Agri-bussiness sector - enabeling a very few people to grow (grain in particular - either directly eaten or fed to animals for meat) for the vast number in cities. it allows the processing and many many, journys that are made by the food produects to take place and is central to the distribution of the finished highly refined food products that often come from miles away to make up the main part of many modern peoples diets.
I could go on but wont.
I STRONGLY suggest that everyone should got to "theoildrumdotcom" to read about peak oil, the many arguments relating to its potential effects, plausibility, proposed technilogical escapes and why they (largely) arnt feasible and a wealth of other infomation.
Alternatively, and perhaps better as consolidated fact opinion and a dramatic that relatively accurte wake up call, visit
http://www.lifeaftertheoilcrash.net/ for the long and comprehensive summary.
(let it be noted i have no affiliation or investment in either of these two sites - they are mearly the best and most usefull imediate resources i have come accross on this topic)
Jeremy Daniel Meadows. (Jed).
Those who walk in truth and love grow in honour and strength
It can easily kill a person but will only knock a small amound of plaster off the wall. Now that's reasuring to know isn't it? Maybe we should all have one to fight the Plastic People off when they come for me carrotts. 
