What Ian said is very true. There remain two huge oil hungry superpower countries to compete over the miniscule oil and gas resources left on the earth. Whoever controls that will probably remain the superpower, and the liklihood of wars over that remaining puddle just increases day by day. I've read that the first showdown will probably happen in the Pacific. Right now the US controls all waters up to the coast of China. Apparently China doesn't care much for this, and is currently busy preparing its Navy to obtain more control of its coastal waters. The US's "no compromise anywhere anyhow" attitude probably won't help things here.
Apparently solar had a lot of possibilities, but many US oil companies bought up the copyrights for solar technology (again, I read this somewhere), and they continue to sit on them. As long as oil interests rule the US, we'll probably remain stuck in the gas/oil guzzling economy. They simply have too much to lose right now to convert to alternatives.
Lastly, gas sits around $2.70 a gallon (as of yesterday). But $4.00 a gallon doesn't sound too far off.