There's always something that doesn't ring true in these cases, though.
Why, for example, if you were testing some sort of high performance, super-secret mega jet would you send it at relatively low level through some of the busiest airspace in the world? Unless you WANT it to be seen, in which case you just publish a photo through the area 57 press office!
Isn't that the whole point of a stealthy clandestine recce aircraft??? the fact that it can operate in 'busy' areas.
Yeah sometimes it will be seen, but only by a tiny minority that won't be able to describe it, as they've never seen anything like it before and the likelihood of them seeing it again is even more remote. Even then, most people will think they're just talking bull, hence why the 'UFO' culture is actually a benefit to development aircraft.
Despite the 'test' aircraft being witnessed, 99.99% of the world are still non the wiser to it's existence and the reason why it hasn't gone through the area 57 press office.