Do questions relating to the development of QGIS plugins (interaction with the API, c++ and python, PyQT, other python modules, etc) belong on GIS SE or Stack Overflow?
1 Answer
If a plugin-question is primarily about PyQGIS, spatial analysis, some aspect of making a map, or spatial data formats then it belongs on GIS SE.
If the issue is more strictly related to non-spatial programming then Stack Overflow is more appropriate.
I would think the examples you listed would usually fall on the GIS SE side, except for things like "having problems with memory management in Python plugin I'm developing for QGIS".