I'm new to the site, but not 3D modeling. I'm a mechanical/aerospace engineer with over 10 years experience in Unigraphics. I've played with Blender, AC3D, and just about every other option out there, but I mostly stick to AC3D (when I'm not at work on UG). Mostly I use AC3D for modeling aircraft for the flight-sim X-Plane. I also use it for animating aircraft mechanisms (landing gear, control surfaces, etc). I'm also a Community Leader & Moderator over at the X-Plane.org forums.