As a unix geek, I like to see and sometimes browse /usr for various reasons. While I can do it from the command line, it would be nice to be able to do it in the Finder. Thanks to information I found in the article Top Ten Mac OS X Tips for Unix Geeks I was able to make /usr not hidden anymore. (The article is from 2002, but this bit of imformation is still relevant.) The following command removes the HFS+ hidden attribute and that lets the Finder show it. As the full path below implies, you need to have the developer tools installed.
# /Developer/Tools/SetFile -a v /usr
You probably need to restart the Finder after you do this. If it has seen the metadata for something (e.g., you browsed /) it’s cached and I haven’t found a way to invalidate that cache short of restarting the app.