I've seen and created some cool library features in the past. At one point I worked for an optical manufacturer and came up with a library feature that allowed you to bounce a beam of light off of mirrors, and would model the path as you went.
Does anyone have any cool library features you use or would like to share? Or ideas for library features you would like help developing?
Or how about Smart Components? That is some potentially useful functionality I haven't had much practical use for yet. Anyone have comments on this stuff?