I grok viewlets in Plone 3

Thanks to Martin Aspelli's handy book and some notes I found via Googling and my own Zope 3 experience, I started to find success with viewlets. I need to read Mikko's nasty jibe on the subject and see if I still am in his corner. My impression is powerful, but admittedly hard to tweak without tiny issues that take annoying time to fix.