[belese]

you should place your script here :
/home/xbian/.xbmc/addons/
and it should work with this.
i've done some services, and they runs from there

the path /usr/local/share/xbmc/addons/
is normally reserved for default xbmc addon and shouldn't be modified (will be erased at each xbmc update).

otherwise, it was in my plan to integrate it with xbian-config-python,
but not on the first version.
my first idea was to start service when xbmc screesaver is on, and stop when screensaver is off.