The majority here seem to be pointing at users being the culprit, but IT people are just as bad, to wit:
Conversation had too many times by myself (other person speaking first)
"LDAP isn't working"
"How do you know?"
"Entrust is no longer issuing certificates"
"OK, so how is that LDAP's fault?"
"Well Entrust puts the certs into LDAP"
"Yes I know how the system hangs together, but how does what you are telling me mean that LDAP is broken?"
"Entrust has stopped working"
"Yes I know, but what is your proof that LDAP has caused it?"
"It's no longer issuing certificates and the last time this happened it was LDAP"
"That doesn't mean it is this time, lets work through this, have you tried connecting from the Entrust box to LDAP?"
"No"
"OK, go do that then come back and tell me LDAP isn't working"
...
9 time out of ten it is not UNDERSTANDING what is happening or how to test it that is the issue, not that X, Y or LDAP is broken...
My personal pet hate, as others have mentioned, though is "Ping" you an email, my usual reply is "I tried that and just got destination unreachable" or if I am feeling particularly mean, printing off the POP, IMAP and SMTP RFCs and asking them to explain where ICMP packets come into it. Usually they just ask me to send them an email after that