When looking around ingame, it is expected that moving your mouse left immediately makes the view go left.
A delay between input and output is very annoying and for example experienced in some games when turning on VSYNC.
With my current settings ARMA runs at around 60 fps and turning SSAO on or changing its quality has an effect on the fps in the range of 2 to 4, so overall bad performance should not be the root of this issue.
This issue is only present ingame, the mouse cursor in the menu is not affected.
CPU: AMD Phenom II X4 965
GPU: AMD Radeon HD 5870