Don't forget to replace USERNAME both places where it appears with the proper username (case-sensitive, usually all lower case), and also replace DOMAIN.EXT with the proper domain name, always in lower-case.
So if I switch to phpcgi and change the ownerships to the files all the users' php scripts will continue to function as normal? Even the php embedded in html files?
When I embed php in html files I use a php extension. Do you?
.php files should continue to work, but of course I have no idea of there are some commands which will give you problems. We've not had any problems so far.