The ease with which a user can inadvertently or deliberately submit a
web form multiple times is a persistent problem with web applications
and web forms.
Typically this problem arises when a user attempts to submit a form and
the server does not immediately respond to the request. The delay can
be due to network traffic, high load, or a particularly complex action
that must be completed. In any event, it does not take long before the
user begins to wonder if they actually hit the button and they click it
again just to make sure.
If your application is not properly designed, this can lead to multiple
identical records, or actions being processed more than once. Sometimes
with undesirable side effects (like multiple billing).
Read the rest and get the plugin at…
http://www.sciwerks.com/blog/2006/10/23/double-submit-protection/
_Kevin