I've been meaning to post about this for a while now, because this product is as close to black magic as I've ever seen, even though I know the theory of how it works. My wife and I picked up a Brown Sugar Saver from Sur La Table while at our local mall a few weeks ago. We had a container of brown sugar that was literally as hard as a rock. Various metal implements were unable to pry the concrete-like material from its container, so we decided we'd give this a try.
The Brown Sugar Saver is simply a piece of terracotta pottery; nothing more. You soak the small medallion in a dish of water for 15 minutes, remove it, blot it dry with a towel, and place it directly in the container with your brown sugar. We did this, and in the morning found that our brown sugar was just as soft and pliable as it would be had you just opened a fresh bag of the stuff! Needless to say, we were really surprised. It only cost $4, and has solved an annoying problem that I've lived with for far too long. I highly recommend this thing (you can buy similar ones in a number of places).