After some nagging from an colleague I used to work with at Lionhead I decided to use Fraps to make a small movie of my little game in action.
You know what I found?
The framerate drop introduced by Fraps when recording the movie totally blew the numerical integrators used in my AI update functions - things seeking paths were having a little difficulty staying on path because the steering functions just lost numerical stability.
Where I work currently the game engine uses a 100hz update for all AI and physics. I used to be against this but now I have seen my own numerical instability and what that looks like - I am all in favour of it now.
So, now I am on a quest for a decent method of achieving a 100hz update...