I agree with CaptBevvil. It's simply a matter of economics. When hydrogen becomes cheaper than oil, we'll see hydrogen technology slowly encroach upon the market. A little while longer, and hydrogen will be standard. This won't happen until oil starts costing more than hydrogen.
The problem is, hydrogen doesn't occur in large quantities here on earth. It would have to be split from water, which takes a lot of energy in itself. There are currently two schools of thought on how to do this on a large enough scale to meet America's transportation needs. The first is to create a few huge nuclear facilities solely devoted to doing it, and the other is to equip every gas station (or maybe even automobile) with the technology to do the same thing on a smaller scale.
Both are viable, but both cost more than $3.00/gallon, unlike oil. That's why we
use oil. No, the economy won't crash. We'll just be devoting more of our budgest toward transportation (or if you're smart, you'll start bicycle commuting
).