Binary package hint: nautilus
(FreeDesktop base directory specification):
"$XDG_CACHE_HOME defines the base directory relative to which user specific
non-essential data files should be stored. If $XDG_CACHE_HOME is either not set
or empty, a default equal to $HOME/.cache should be used."
To make things like backups easier, nautilus' gnome-video-thumbnailer should
place its thumbnails somewhere in ~/.cache. This would also ease the
development of automatic cleanup tools (see linked specs).