I've been dealing with an ongoing problem with my early 2011 MacBook Pro. I have a 250gb SSD as my primary drive, and I swapped out the DVD drive for a 1tb drive. I've moved a bunch of things over to the secondary drive, but still encounter wild swings in the available space on my primary drive. Yesterday I was receiving warnings that my disk space was critically low, and it was down to less than 1gb of free space. Today it's back up to 20gb of free space. I've used Grand Perspective to see where the space is going, and I see most of it is being used, but I can't see where the ~20gb or so of free space disappears to so quickly. Since I began typing this message, I've dropped ~2gb of free space. Any suggestions on how to identify where it's going?