The Earth finished another rotation around the sun in 2007—just about. At midnight on December 31, it was actually about 400,000 miles short of where it had been a year before, and that annual shortfall is why we have leap years, explains the St. Louis Post-Dispatch. Leap years like 2008 have an extra day to ensure the calendar and seasons keep pace.
The old Julian calendar was a fraction off, which Pope Gregory XIII fixed in 1582 by taking a few leap years out and removing 10 days from that year's October. The Earth is gradually slowing down and making fewer rotations as it orbits the sun, but it will be thousands of years before the Gregorian calendar needs any changes.