I would definitely bike everywhere if gas got to a certian point. I'd probably have to switch jobs or something though. Biking 30 miles just to get to work a little far, particularly on a mountain bike. I did notice a few more people driving a bit slower since the message board changed. Ironically it's usually the people driving small compact cars and such.
I saw this article about people refining their own bio-fuel. Makes me want to go out and buy a TDI VW and a deep fryer.
People care, so long as they don't have to sacrifice too much to meet its needs.
BUT they've been backed into a corner by vested interests. Our cars wouldn't be near such a burden politically and environmentally if they were either very efficient, alternative fueled, or both. But the oil and auto companies and federal government have other plans.
A recent thread on another forum brought up the topic of denial. It probably does play a role since we are relatively early in the game right now. Accepting the possibility of dramatic change is not something humans do well, in general. We resist passively by going on about life as we always did, and sometimes we resist actively by doing the exact opposite of what we know we should be doing. Most people fit into the former category, and a good example of the latter is the person in a large SUV or truck who tries to drive up the tail pipe of every Prius and Insight on the road. That's not plain stupidity, it's an act of rebellion.
People will change with time depending on how things go. If something very bad happens in the middle east and we come up short of fuel, you better believe people will change relatively quickly. But that requires necessity to change, not just higher prices than we are used to. Pure economic pressure will result in a longer transition.
So the short answer is this: The average North American will care when he is forced to care, like the Europeans with their $6 gasoline. It requires pressure beyond the point at which we can still talk ourselves into believing that everything is OK. We will get there.