In the USA, the clocks are also changed in spring and autumn. Exceptions to this rule are only a few parts and territories of the USA, such as Hawaii, American Samoa, Guam, Puerto Rico, the Virgin Islands as well as the state of Arizona (where, however, in the Navajo-Indian reservation summer time is indeed used).
Until 2007, US-summer time (Daylight Saving Time) began on the first Sunday in April, thus a week later than our conversion date, and ended on the last Sunday in October, just as ours does. Starting in the year 2007, American summer time is a total of four weeks longer: It begins three weeks earlier, namely on the second Sunday in March, and ends a week later, namely on the first Sunday in November.
The US government expects to gain, above all, economic advantages. On each of these additional "summer days", energy in an equivalent value of 100 000 barrels (approx. 16 million litres) of oil will be saved. A study is to show if this will indeed be the case. In addition, a lower crime rate, fewer accidents, more economic growth as well as more time for leisure activities is expected.
Information by NIST, the American metrology institute, on this subject