The problem of evil (see this post) can be briefly summed up as being the problem of why, if God is all-good and all-powerful, should evil exist. Theologians have come up with many ingenious ways to get around this problem (e.g. free will, needing evil to appreciate good, etc), which tend mostly to abstract evil as being a general concept, which can then be regarded dispassionately as a means to a greater end.
However, regardless of the plausibility or implausibility of these arguments, for me the problem comes in applying them to any specific instance of evil. If any of us had God's knowledge of an event, and his power to intervene, would we stand by and do nothing? An example could be the September 11th attack - if you personally knew such an event was going to happen, would you not do all that was in your power to prevent it? And if you did not do all you could, would you not be judged as guilty by your inaction? How much more so then God, whose knowledge is perfect and power is infinite?
I came across this article the other day: The Tale of the Twelve Officers, which takes all the arguments I have heard to try and justify God's apparent inaction in the face of evil, and places them in the setting of a particular evil act. I challenge anyone to accept any of the arguments given by the officers in the story as being remotely justifiable excuses for inaction in the face of a specific evil act.