Why do application windows lag behind when dragging?

I have a slight problem, recently my Macbook has become somewhat slower than normal in the fact that when you click to drag a window around the screen, it lags behind the mouse by at least 2 seconds, it moves smoothly without any freezing and its following the mouses path but isn't under the mouse pointer as I move it because of the 2 second delay... It does this both with power and on battery. What might cause this and can it be fixed?