I think most of them are military air craft that are being tested, remember the Stealth Jet? The Bomber that looks like a black triangle, well for 10 years these black traingle UFO's were spotted until the US finally unvield there secret bomber. Also there was a plane capable of going i think its 2000mph(the blackbird,looks a lot like the Xmen plane) or something like that that leaves circle smoke trails and sonic boom sounds as it fly's past this was witnissed a lot of times to until it was unvield and every stopped panicing ect.. But i also think that there must be at least 1 UFO sighting that is genuine, i mean there is billions of galaxies, each galaxy can hold between 1million-1billion, i mean we cant be the only life form can we?

Well, I've written a large post about this on my clans forums a while ago and I actually hoped it'd somehow get here too to discuss. Actually, I'm VERY interested in this topic. Not in the roswell part of it but in the sciencific one. Anti-Gravity IS possible and has already been measured by scientist. Only a few few milligrams but still enough to verfify the effect. Of course, this isn't nearly enough to make a disk fly. It has been confirmed that the Germans had "Flugscheiben" Eng. Fly-disks in the end of WWII which didn't shoot but which confused enemy pilots thus making them crash by glowing strangly. I really don't like conspiracy theories but theres no way the Americans wouldnt have captured the secret UFO's (I don't like that name either) after the war if they existed. A few links I've gathered about this topic:
http://video.google.com/videoplay?docid … 8311217291 Good video
http://fast-geheim.de/html/rundflugzeuge1.html German, sorry
http://www.kheichhorn.de/html/body_entwicklung.html German, sorry
http://www.reichsflugscheiben.de/ German, sorry
I guess you've all seen the the so-called alien pictures of the guys with the oval head. It is rumored that those guys were 'test-pilots' for captured German fly-disks after the war which couldn't really take G's. A lot of the stuff that you can read is total bull, other stuff is true again. As I said I really don't like conspiracy theories, lies or some freak out stuff which you just want to be true but yet I believe that the Germans had such flying disks in the end of WWII and I'dont believe there has ever been any extraterrestrial contact at all. If there were flying saucers then they were made on earth.
In a German sciencific discussion forum I've read about several theories a proper Anti-Gravity engine could function but I can't go into detail now, it would just take too much time. Maybe we get an interesting discussion going...

wormholes?