I would want to be able to define and use note levels in a way similar to commonly known "log level".
note right INFO
note right WARN: warn text
note right ERROR: error text
Then, depending on a skinparam, for example:
skinparam noteLevel WARN
I would display all WARN notes and hide all other notes.
skinparam noteLevel should also support NONE value for an ability to hide all notes (as requested in http://forum.plantuml.net/7011/a-parameter-to-disable-hide-all-notes-in-a-diagram
By default, i think, all notes can be considered as INFO level