This has been bothering me for a few years now, and I'm wondering if anyone has a solution.
Whenever I try to put a Motion file into Final Cut, the unrendered video looks fine. However, when I try to render or export it, it renders as a black screen. This problem can be avoided by exporting from Motion and then putting the resulting .mov into Final Cut, but it's a pain and makes it difficult to quickly change things in the Motion file.
If it helps, I'm using Final Cut Studio 2 with all of the recent updates installed on a 2008 Mac Mini running Snow Leopard.