I am working with a customer that has a self-signed certificate which has expired.  They have no single signon rules defined.  I created a new certificate and it shows as active.  The expired cert also shows as expired, but the active box is checked.  I don't see any way to remove it.  Do I need to?  Is there anything else I need to do for the new cert?

Is there a way for me to find out if we are currently using a self signed certificate with any of our SFDC applications?  I can see that we created one  (or someone created one for us) a couple of years ago.  I received a notification that it will soon be expiring but I'm not aware of us actually using it for anything.