none...although, I used to wrench at a shop. Today...I even build my own tools if I need to. I was just thinking about buying a small machining lathe.
I believe knowing and being comfortable with the mechanics of your ride is one of the best things you can do. I always scratch my head when riding with people who don't know how to do something as simple trim out a derailleur cable on the fly.
That being said, only do what you feel comfortable with. I know the mechanics at my shop began to offer repair classes to the public after I left.