On some webservers if the administrator is a paranoid beep, PHP files that are world writable are disabled (the Webserver won't read them).
These Servers should aslo be setup to allow SuExec, in which case chmod'ing to 755(or 700) should suffice,
So the preferable permissions are in the following order
700 -- if SuExec is fully setup and the file will not be accessed directly(eg config Files)
755 -- if SuExec is isntalled and the file will be accessed directly
777 -- if SuExec is not installed, in which case your contents are insecure.