Wow, stratagos. We really CAN'T agree on anything.
First of all, the term "UFO" is widely abused. Unidentified flying objects DO exist. I won't dispute that. People spot man-made objects and fail to identify them correctly ALL THE TIME.
Second, aliens do not exist. If there is a "Conspiracy", it is obviously covering up experimental military projects, not alien life.
Third, people should keep their noses out of the DoD's private business. If the government is hiding something, that means that it would be harmful to our interests if someone revealed/discovered that something. The government doesn't hide stuff for the hell of it.
Fourth, 99.9% of all "UFOs" have been explained as weather balloons, satillites, PhotoShopped, or declassified by the military, like the Roswell UFO Incident: "In 1994/5, the Air Force published a report which concluded that Mogul Flight #4, launched from Alamogordo, New Mexico, on June 4, 1947, was what crashed near Roswell, New Mexico, and formed the source of the debris which sparked the Roswell UFO Incident." (Wikipedia/Project Mogul)
And for the 0.1% that hasn't been explained? Obviously still classified by the military.