With the caveat that I haven't used it, I did stumble across File::chdir recently, which supposedly lets you localize $CWD to change directories and the change is reverted as soon as the localization goes out of scope. Seemed handy as a way of letting something else keep track of the old directory instead of doing it yourself.

Again, unlikely it's thread safe -- almost no directory change is, I believe -- you just have to use absolute paths for everything if you're using threads (or fork on Windows).