Understanding net energy is important to understanding Peak Oil. The main reason we pump oil is to burn it for energy. As we substitute lower EROEI oil for depleting higher EROEI oil, the amount of energy available decreases even if production stays constant. This can happen on the production side (i.e. deep water oil has a much lower EROEI than East Texas fields had). It can also happen during refining (i.e. coking heavy oil is more energy intensive than fractional distillation).

It is insufficient to focus on raw production numbers, because raw production doesn't capture any of this. If production is flat and EROEI is declining, then net energy is declining and prices will go up.

In addition net exports is an important part of the picture, at least for countries that import oil. IMO, the combination of the two -- declining EROEI coupled with declining net exports -- is why oil prices have risen so far, even as the G7 economies slip into recession.

Declining EROEI is nearly impossible to quantify, however. It also involves more than oil, e.g. natural gas is a significant input into both Canadian tar sands and ethanol. But I think the effect is real. We are feeling it. It is going to get progressively worse. And it is nearly entirely below the radar. I don't know how to make the case in more than arm-wavy sorts of ways.