I’m doing some theming work on my team’s first Plone-based site. It’s the first real (i.e., useful, concrete, for-my-job) Plone work I’ve done.
For the first time, just now, I knew how to find a viewlet’s linkages and guts. Without thinking, I went looking for the configure.zcml and common.py files… I’m starting to know what I’m doing!
Seek Nuance 
I’m not sure I’m at that point yet, but it’s encouraging that I knew exactly what you were talking about 🙂