they seemed to be expecting dust on the hazcams, which i think i remember them saying (it was very early..) still had covers on them for the first shots.
Somewhat related, and perhaps my favorite facepalm moment in space probe history: "...the titanium lens cap on Venera 14 landed precisely on the area which was targeted by the soil compression probe." (http://en.wikipedia.org/wiki/Venera#Venera_camera_failures_a...)