MongoDB - Delayed Secondaries

Setting up a delayed secondary is a good way to help you recover from a fat-finger error.
In the picture below, you'll notice that a test object can be found on the Primary, but not yet on the delayed Secondary.  To accomplish this, you need to set 'hidden' and 'priority' and 'slaveDelay' attributes.

More about recovering with a delayed secondary by tweaking the OpLog:
http://stackoverflow.com/questions/15444920/modify-and-replay-mongodb-oplog/15451297#15451297