Hi, The graphic is realy nice and i realy like your grass.
I have get a little problem with your culling system surely.
Exemple in the joint machine if i set the scene to wireframe when i back to the normal all parts normaly hide back the camera is not displayed anymore. The smoke over the machine is culled so quick when i'm close to it. The machine joint is not stable whit high speed, the machine make many little jump and here the wheels have coming totaly on the bad axis. The other little problem i have get is whit the advanced vehicle, in general it working good but when i try to go faster and when i turning the vehicle reacting strange like a boat on a river.
I think this problem is related to the inertia and friction. I have get a other strange result with the vehicle i have pass in a box and the box have never move and the vehicle have continue normaly too, when i have turn back and pass in the same box it have start to collide normaly no idea why.
Other stuff looking nice, and i very like the graphic and i have good fps on my old computer. Surely you know already about the problem i talking upper if no i'm happy if it can help you.
PS: I don't know why but the demo joint machine show a message randomly, thanks to have try..........
Edited: Sorry about the wireframe and culling problem, i'm wrong it hapening when i pressing F, it is surely something implemented from you.
I have surely press F by error and i have think it coming after have set the wireframe sorry again.
Here a quick video with the machine problem, with fraps enabled in background the fps is a lot more slow but the problem happening faster with high fps when fraps is close.
http://www.dave.serveusers.com/SansTitre01.wmv
I don't have make video with the other vehicle problem because with fraps the fps coming slow and it is more hard to reproduce the problem.