You know, this BP oil spill is going to be good for the environment.   Seriously.

It's going to be the worst spill in history by the time it's over, the entire Gulf of Mexico is going to smell like a truck stop, and all those pretty beaches are going to be fouled.   Thousands of people will be thrown out of work and entire industries and ecosystems in the area will be destroyed.

The thing that many people haven't thought through, though, is that this is going to kill US offshore oil production.  My guess is that no new permits will be granted for a decade.   Maybe two.   Arnold has already announced that California won't go there, anymore.   My guess is that most areas will agree with him.
 
This is going to force the US to electric cars more quickly than they would otherwise have been adopted.  People who hate nuclear energy are going to think of the BP spill and accept more power plants because the fossil fuel alternative is so repugnant. 
 
Development of better battery technology will become an urgent matter as governments move aggressively to phase out gasoline and diesel fueled vehicles.

The switch to electric vehicles that would have taken many decades will now probably take much less time.

And the Gulf of Mexico will recover.   It'll take a long time, but it will.