I hate to keep continuing this thread, but ...
You have to look at it from a management practices standpoint and its
relation to our societies current facination with suing each other.  Use of
drugs is still a crime and not having any kind of drug testing policy can put
your institution in a very awkward [understatement :-) ] position if the
dinasour falls on a patron and the last employee, or volunteer for that
matter, who touched it tests positive for drug use.  To put it mildly,
they're going to sue the pants off you.
The same goes for background checks.  God forbid one of your employees
fondles a child or something similar and a background check revels a history
of criminal activity.  Just think of the negative publicity and lawsuits that
could result.
Institutions such as museums and librarys which deal with the general public
on a daily basis need to protect themselves as much as they can.  We seem to
put much more emphasis on safeguarding artifacts than on the security of the
institution itself.
Many messages have aluded to Big Brother Watching, I think it's more a case
of being a prudent operator and protecting yourself to the extent possible.