Kurt Cobb brings up an important point in the peak oil debate: the role of risk and probablity. He explains that when the consequences are severe, we will do our best to mitigate the risk even when the odds are low that something bad will happen. For example, most of us have fire insurance even when it is unlikely that we will ever have a fire.
So when it comes to peak oil, which has potentially very severe consequences, why not behave as if it will happen even if we can't predict when it will happen? Especially considering that every year that goes by increases the odds that it will happen this year. We may not be sure that the doomers are right, but it is better to be safe than sorry.
For a clearer explaination than I can do here, go read his essay.