CAD companies leaving behind VB,VBA,LISP,C++ and going for .net (VB/C#) for customization of CAD softwares. But difficult to find good training material! very few events, webinars on customization available.
It's amazing experience to get models using programming language. Many design engineers feel like moving toward's customization when nothing remains new in CAD designing software, Just routine work all the life!
All not lucky enough to get company trainings. May be below links help somewhat to get started with customization. AutoCAD, Inventor, SolidWorks, Catia, Pro/E Customization.
Hope CAD companies do get into some webinars on API's training soon.