Never mind. This space re-disappeared within about a week. Bummer. On the plus side, I was able to use the Scanner app (http://tinyapps.org/file.html) to locate some old iTunes and Safari installers in various temp folders.
Recently, I've been running low on HD space. Using Scanner, my HD-as-a-pie-chart-viewing tool of choice, I've often noticed just how much space my winsxs folder takes up. I've Googled it a number of times only to find that it isn't the kind of place you can just go and delete things. However, I decided to try it again, and fortunately, I stumbled upon this helpful post.
Using the vsp1cln.exe utility saved me almost a GB of HD space - extremely valuable. Of course, my winsxs folder is still huge, and it's only a matter of time until I run out of HD space again, but this just might be enough to get me through until my next computer.