I see that the new 2011 Ford Fiesta that is being released later this year is another snoozer as far as MPG goes - mid 30s. The European diesel Fiesta "ECOnetic" is rated at about 60+. The word is that such a car is a polluter by U.S. standards, so you wouldn't be able to register it in the U.S., but I don't know if that is B.S. or true. Can one import such a car and set it up to meet emissions standards in the U.S., register it, make it legal? Or would such modifications necessarily destroy MPG?

One-off emissions upgrades aren't cost-effective - you'd spend millions of dollars to get the car to pass, and run through the required durability course. You'd also need to deal with the (subtly) different safety tests (i.e. air bag and restraint systems), some of which require crash testing.

Most EU countries have traded off the higher NOx and particulate emissions for lower CO2 emissions - and to a degree traded off some safety aspects for the same goal. There are also cost considerations - Diesels typically cost more, and European fuel prices make the cost more easy to justify. One other factor in EU take rate for Diesels is the relative fuel pricing - EU typically gives Diesel a significant break on fuel taxes;according to http://www.eia.doe.gov/emeu/internat...ces.html#Motor the difference is about $1/gal, where Diesel costs less. In the US, Diesel costs about the same or even a bit more than Premium.