Those "UFO's" you've seen may have been ARV's (Alien Reproduction Vehicles), crafts made by the government replicating actual alien technology, or it was actual aliens. They are capable of super-luminal speeds (faster than the speed of light). Using zero-point energy, the same energy thats surrounds us everywhere, to control gravity (anti-gravity).
If these technoolgies were declassified and used publicly, almost all poverty and pollution problems will be a thing of the past. We are already using a tiny bit of these alien technologies in our everyday lives, such as infared, night vision, computer chips, lasers, microwaves, bullet-proof vests, cell phones, television, and much much more. All these new technologies suddenly popping up out of nowhere since the 1940's-1950's? (ahem, about the time period of the Roswel incident)
It is believed that the secret government is actually communicating with extraterrestrial intelligence.
The US government is spending over $50 billion a year on the study and production of this technology.
Still skeptical?
http://www.disclosureproject.com/
They have over 400 witnesses and people who were actually part of the secret projects testifying to their experiences on video.
http://www.topsecrettestimony.com/6monthsummary.htm is a list of 47 of the witnesses.