Origins of modern Daylight Saving Time
Founding father and kite enthusiast Ben Franklin is commonly credited with DST's invention, but this isn't entirely accurate. During his time as envoy to France, Franklin did publish an anonymous letter in which he presented the concept of rising earlier in the morning to take full advantage of the sunlight (and save on candle wax). That said, Franklin's letter is largely understood to be a satire -- he also suggested taxing window shutters and firing off cannons at sunrise -- and he never publicly pursued the idea beyond this publication. He did invent the Glass Armonica, though.
These days, DST is commonly attributed to one of two men (depending on who you ask): a New Zealander named George Hudson, or an Englishman named William Willett, both of whom proposed the daylight-saving idea independently around the turn of the 19th century.
It wasn't until the onset of World War I that DST was officially adopted on the national level, however -- first by the German Empire and Austria-Hungary, who called it "war time," and then shortly thereafter by the British, who gave it the more pleasant-sounding name of "summer time." Both sides had good reason to implement this time shift: in a period as rife with turmoil as WWI, optimizing usage of coal resources and daylight hours was key. The shift was generally repealed once the war ended, but got fired up again once WWII started up, implemented year-round in some countries (like the USA) and summer-only in others.
Once WWII ended, America's official nationwide policy on DST was repealed yet again, but some states kept the dream alive. A standardized nationwide DST was finally established in 1966, largely because having different states operating on different times in different time zones is, in official terms, a giant clusterfuck. The new DST ran from the last Sunday in April to the last Sunday in October; President Reagan made some adjustments to it 20 years later, and we only recently arrived at the modern US standard of March - November in 2007. In other words, we'll be due for a change again in 10 more years.
It's important to note, though, that not every state adheres to DST: most of Arizona's been exempted since 1967, and Hawaii was never part of the Uniform Time Act. Aloha, bitches!