I can't really say I've made anything "cool". I use AutoCAD for work and school. At work I design Precast Modular Block retaining walls. Right now for school I am putting together a complete set of conceptual building drawings from scratch. I've been using AutoCAD for about 10 years, and could pretty much run it with my eyes closed.
Last year I took a engineering class and we had to make a wind power device, which was kind of fun because I got to make it after I made it in AutoCAD.