FWIW, once I saw several UFOs. I happened to be an a science fiction convention in Atlanta, so I was tempted to walk away since: 1) they might be part of the festivities, or 2) I might have been in a suggestible state. But I stayed and observed them more closely...
It was nighttime and they were hovering in the black sky over a large building several hundred years away. They didn't act anything like airplanes or helicopters. They held still in the air, or changed direction abruptly: every now and again, one would dive in a straight line toward the building, then disappear, only to reappear when streaking straight up from it. They were silvery in appearance.
Finally I realized what I was seeing: they were birds, circling above the lights (when they flew toward me, they appeared to hold still), diving down to eat insects and moving out of the building's lights, then moving back into them as they swooped up. I never could resolve them into bird shapes due to the distance, but after extended observation, I was able to recognize the scene as a whole and thus tell that they were birds. It was surprising: one moment, their actions were a total mystery - the next, they were clearly birds like I'd been observing my whole life (though not under those odd lighting conditions).
So, I do believe in those few-seconds-long UFO films shown on TV. I believe that an inexperienced observer (as I was) saw something that he/she couldn't explain (as I did) and related how it didn't match any usual phenomena (as I did above).
The difference is, I stuck around and kept thinking and trying to figure things out and eventually did recognize the unusual phenomena that I was seeing as normal, terrestrial activity. The stuff usually shown on UFO TV shows consists solely of the type of uncertainty that I had before I understood what I was seeing (and which is thus, for no justifiable reason, linked to extraterrestrial spacecraft). I guess that anyone who figured out what they were really seeing didn't bother trying to sell their footage - only those who never did continued to do so, presumably in good faith, and thus are (literally) selling and promoting their uncertainty (or, to be more harsh, ignorance).
Thus, I do believe in unidentified flying objects (which I saw until I identified them), but I don't believe in flying saucers. Good for the MoD for investigating, but I for one wouldn't be surprised if an ordinary, terrestrial phenomenon explains it (there are presumably a lot more birds and such on Earth than flying saucers).