I happen to notice this. I created a google spreadsheet and I shared it among three people. I wrote a code for onEdit() trigger. I set the trigger(Resources->all your trigger-> create new trigger). If another user opens the google spreadsheet, the trigger I create is not available for him. He needs to set the same trigger again.
My question is: Is there anyway I can set trigger for all people for whom the spread sheet was shared? Is it possible? Or is creating a trigger user-specific?