Had a problem with multiple instances where bone setting was stomping on top of each other. The trick was to make sure I set the bones before the EffectPass.Begin() call to make sure the triangle batch is rendered using those bone matrices. Here is an image of 100 robots all animating. Render time is still good! I'm also trying to be really careful about reusing and not creating objects (which I hear really kills you on the xbox). Next stop is to get 2d rendering up so I can make my extrusion editor.