There are lots of trucks in the Denver area that run on diesel, so for an American city a good percentage of our gas stations carry diesel. They are all also required now to carry the ultra-low sulfur diesels that are required in most BMWs. The reports I have read said that BMW is still on track to begin selling the 335d here in the states next month. Colorado is not one of the states that use California emissions and therefore we have been able to buy vehicles like the TDi VWs where in California, they can't sell them there.
However what is different here from Europe is that Diesel typically costs more per gallon than even premium gas since it is taxed heavier. So sometimes the cost of diesel does not offset the benefit you get from the higher mileage you can achieve.