wouldnt be kind of cheating if trackir stops head shaking from happening?
 

do guys with trackir experience headshake?

i cant see how

Depends on what kind of shake it is. A lot of head shakes move around the center point, which doesn't ruin gunnery and is easy to adapt to. It would be cheating if real translation of the head is removed - I don't know if that's possible with smoothing in trackir though, it's programmed into the game.

Yes we do.

but for example if the shake pushes the head down for ten seconds

are you rising your head ten seconds till you hit the ceiling ? :)

yes, when pulling intense G's I have to move my head upwards to be able to see over my aircraft's nose :p