(throwaway account)
I really, really dislike this method. If there's a problem employee, deal with that employee. Don't send blanket emails to everyone. It (in my experience) does not work since the person that's actually doing something offensive usually doesn't realize it, and it just confuses all other people working into wondering if they somehow are to blame.
This tactic seems to be really common where I work, and all it seems to lead to is confusion and anger with management because they're unclear. It's as if everyone is being lectured for something one person did.
If I've said something inappropriate, please let me know. If not, leave me out of it so I don't have to worry that I might have. This stuff creates a lot of unneeded stress. It's one of the reasons I'm looking for a new job. Seriously.