From the 2011 MD Wikipedia article:
2011 MD is an Apollo asteroid, which is bound to pass relatively close to Earth’s surface at a distance of about 12,000 kilometers (7,500 mi), roughly 32 times closer than the Moon, at around 17:00 UTC (13:00 EDT) on June 27, 2011. Although initially suspected of being space junk, subsequent observations confirmed the object is an asteroid.
Since the object will appear close to the sun in the sky during the event, observing it will be possible only for a brief period a few hours prior to the closest approach. Backyard astronomers will be able to observe it with telescopes from Australia, southern Africa, and the Americas.
It was discovered on June 22, 2011 by the Lincoln Near-Earth Asteroid Research (LINEAR) pair of robotic telescopes in New Mexico and, according to rough estimates, its length is between 10 and 45 meters (30 and 150 ft).
Emily Baldwin, of Astronomy Now magazine, is quoted as saying there is no threat of collision and, should the asteroid enter Earth’s atmosphere, it would “mostly burn up in a brilliant fireball, possibly scattering a few meteorites”, causing no likely harm to life or property on the ground.
Dagbladet.no provides the point of view of the asteroid as it buzzes the Earth. (Click image below for full, animated image.)
Sky & Telescope Magazine writes about where you might be able to see the asteroid as it passes by.