For some reason, one of the folders inside my Applications folder keeps getting hidden. I’m not sure why this happens, but I suspect it’s a side-effect of updating one of the standard applications that I use.
In case this happens to you, and you want to make a hidden file visible again, then the simplest way to do it is to do:
/Developer/Tools/SetFile -a v YourFileOrDirectory
Obviously, you must have the developer tools installed to have this command available.