Activating the plugin via Network-Admin doesn't work. The plugin configuration shows up in the BEs of the individual blogs but using sharethis_button(); function in a template returns nothing. I think this is due to the $widget variable on line 607 of sharethis.php being empty.
Activating the plugin on each individual blog works but is really bothersome. Also, there is an error on line 593 where mangage_options should be wrapped in ''.