I was a complete skeptic about the fabled 'black helicopters' until I saw one with my own eyes.
It was in broad daylight, not two hundred feet off the ground. It was completely silent and totally black. The blades turned so slowly that I couldn't understand how it stayed aloft.
My brother was with me, and saw it too.
Well, that’s certainly interesting. The main rotor of most full-size helicopters rotates maybe 8 or 9 times a second. although one very large Russian prototype (never in production) was less than two times per second. The modified Black Hawk used in the Bin Laden operation may have had more and quieter blades than a BH normally would and was much more radar stealthy, but the basic blade mechanics were not thought to be anything special. I have no idea what you saw.