Oh, you're absolutely right about that. What I've done, usually, though, is render individual elements when they need to cross one another. But you're right, there's no substitute for real 3D motion blur when it's detailed like that. I've been able to fake it with ReelSmart for many applications, particularly when speed of render is important. I'm actually very pleased with the look of Carrara's motion blur (though I haven't upgraded to CS5 yet, so I'm only speaking about CS4). And it's motion blur that can sell a CG shot where it might otherwise fail. Cheers!