Notes may be set to use differently shape icons in Map view, i.e. other than the normal rectangle.
Shapes are still used for notes displayed in the viewport of an agent or container.
The shape of agents, containers, and adornments remains fixed; they ignore the $Shape attribute if it is set by the user. Thus a visible shape can only be set for a note with no children.
Shapes are probably best reserved for special occasions/purposes, in order to emphasise exceptional or unusual notes. Otherwise, maps may become a little busy.
From v5.5.0, shaped adornments are also possible.