Scott Carson has a pair of posts that deal with the problem of evil, the second part being here, in specific answer to a commenter. SF Matheson refers to the first of these, and has some good thoughts of his own, over at Quintessence of Dust.
All three of these posts are thoughtful and worth reading, and it's on a topic which I often feel myself to be peculiarly ill-suited to address. You see, perhaps I'm a terrible, heartless sort of person, but the "problem of evil" doesn't necessarily bother me much. Sure, there are things that have happened in my life that I have desperately wished, as I saw them coming or once reality sprung them on me, would not come to pass. I'm sure all of us have experienced things we wish hadn't happened, and have heard about things elsewhere in the world that we wish were not the case.
And yet, I must say I don't quite get the mentality which sits back and demands, "Why didn't God step in and stop this, if there is a God? Why does God let children starve in Africa? Why does God let people get leprosy? Why does God let children be born to families that can't afford to feed them? Why does God let hurricanes wipe out people's homes?" And so on, and on.
I guess the idea of God as super-nanny who steps in and fixes everying, "Oh, I'm sorry, did that tsunami knock your house over, I'll put it back together." "Oh, did you have a car accident and crush your leg? Okay, here it is back." very attractive. In fact, I actually find it rather repulsive.
According to Christian belief we are each possessed of an immortal soul which is capable of living forever in union with God, should we so choose to do. (Or living forever in howling solitude, should we choose that instead.) We are made in the likeness of God.
So I guess for me the rather obvious answer to the question, "Why are we allowed to suffer?" is: "Because God respects us."
But given the volume of writing on the topic, I'm not exactly the common man in this respect. So go read the linked article, they're really good.