This tip is likely buried in one of my longer posts but will break it out here to give it more attention.  As you purchase more cards be sure to write the purchase date on the card with ink.  Cards don't last forever and if you are going on an important shoot, you may want a fresh card.

In addition, if my shoot is really important I don't want a brand new never-used card or a really old card.  I feel both are just as vulnerable to failure.  So, I would like to have a card that has been through a few cycles of taking photos and the workflow of removing and formatting the card. 

A memory card will last anywhere from 0 days to 10 years or more.  Other than accidental damage, the most likely time for failure is when it is brand new or near its end of life. 

Sorry for the longer tip.