Taking the documentation's word that "it doesn't matter where you put JBoss" I installed it as root under /usr/lib (on a RedHat 7.2 system.) I then ran it as myself (non-root)
There were error messages due to the inability to write to directories under the JBoss heirarchy. It's always a bad idea to assume that the software will be installed to a location that will be writeable at runtime.
To add insult to injury, when I hit Ctrl-C so I could go adjust the ownership of the directory, JBoss went into an infinite loop forking processes until it consumed all available processes. Fortunately with a little finagling I was able to kill it off without bringing down the server.
All is fine now that the directory is owned by a group to which the user running it belongs - but beware new users who don't know they need to be added to that group!