Hi,
I wrote preset with expressions in AE cs4 and it was calculating the direction of layer's motion.
It worked perfectly in CS4.
In CS5 the resulting vector very often has a length of 0 - especially with Nulls that have tracking data applied.
Even though the Null IS moving around.
One workaround I found was to use a BakeTransforms script on the Null layer.
The motion doesn't change, but now for some reason position.vector gives a proper value.
After some testing it seems that if a Null gets tracking data applied, the position.velocity vector for that null is always invalid 
Any ideas?