There is also an API for runtime only/cached stuff, but I don't find it.
Windows:
I am not sure if here is a special way to save data, but I guess we should use this ~/AppData directory, but everything beyond that we should be allowed to do whatever we want.
inside our installation and application data directory, there should be a plugins directory.
I was thinking a little bit about the file structure we should use
Linux:
Mac OS X:
Windows:
inside our installation and application data directory, there should be a plugins directory.