I just came across Charles Stross's posting about the end of fossil fuels boding the end of space exploration (or at least a massive slowdown).
I have to disagree, but the topic brought up a lot more thinking about fuel and our economy than it did about space, at least for me. The man he's quoting calls the end of fossil fuels an, "unprecedented transition," but of course, it's not. Our original fuel (and building!) material of choice was wood. When wood ran out (understand that when we talk about a resource "running out," we mean that it became difficult enough to use that it was no longer the ideal source) we moved on to a combination of iron and oil. Interestingly enough, this lead to a massive explosion in both out economy and technological growth. One could argue that if wood were a much more rapidly replenished resource, we might not have had a space race, or at least it might have come much later.
So, what will the end of fossil fuels bring? We can't really know, but one thing it won't bring is the end of our desire to expand, learn and explore. Will that be in space, or will we decide to go to the bottom of the oceans or into the Earth's crust first? I don't know. We have a lot of 3-dimensional territory to explore and exploit. What I do know is that running out of oil will be a fast process when viewed in the long term, but probably slow enough that we'll transition to something new, just as we did before.