Guys Guys, chill.. i think the pakistan government does not have a good RADAR system ( or the radar watching guy was asleep).
Coming to the technology part,
Firstly: the kind of terrestial radar's that are used normally by any military will not be able to detect any low flying object
Secondly: yeah the coating helps to be invisible to RADAR.
Thirdly: I think the american helicopters rotors were tuned and modified just to reduce the sound levels.
Fourth: If the body of helicopter is "sharply" made, like the "APACHE".... RADAR signatures are reduced.. and as far as the MAIN ROTOR is concerned, if you see it in the "front view" the rotors are actually "flat".. so no problem with the RADAR.... (but if sophisticated spherical dome waveform RADARS were to be used.. then it would have been a problem..)
Conclusion: if you cant find the demon anywhere in the planet!! try searching in pakistan. "Anyone who is in pakistan is unsafe!!(osama)" LOL.. "anyone in INDIA is totally safe(Ajmal kasab- te terrorist involved in the mumbai attack)