I updated to iTunes 8.1 and wondered where my ffmpeg binary went; then I found this explanation, which was spot on:

This may be useful to some people — I’ve solved my problem but it may bite others.

My boot disk is partitioned. The boot partition was too small. I put /usr/local on another partition and made /usr/local be a symbolic link to the real one.

This afternoon, I tried “svn help” (or something more exciting) and got zsh: Command not found: svn

Imagine my surprise!

After a bit of thrashing I discovered that /usr/local/bin is a directory that contains iTunesASUHelper and nothing else, furthermore, /usr/local/lib and other, formerly exciting, directories are no longer in /usr/local…

Seems like the clever install script must check to see that the directory /usr/local exists, and if it doesn’t it throws away whatever is there and makes the directory.

Luckily, it’s pretty easy to recover from a trashed symbolic link, but it’s somewhat harder to find it!

See also.