Since Unity 4 there is HW-Cursor support: http://docs.unity3d.com/Documentation/ScriptReference/Cursor.SetCursor.html however, this doesn't annihilate the Unity inherent mouseInput lag when using, "Input.mousePosition" i know vsync can increase input latency by one frame but the lag between software and hardware cursor feels greater than that -is there any way to get the HW-mouseposition into Unity?
You'll got to live with it: all the stuff within any application on the planet has this "lag". It appears when dragging any custom in-app windows etc. It's just the technical issue (works without a lag only when dragging the OS window).