Just another thing, the standard identd server doesn't support masquerading clients. If you have a linux server with many clients who use irc you might want to install a identd server which supports masquerading on the server.
I don't think it supports spoofing either. Identd usually gives people more information then you'd actually want people to know about your systems. So in some cases it's wise to use ident spoofing for 'security' reasons.
I use oidentd from:
http://ojnk.sourceforge.net
It has a lot of extra options, but there are many other identd servers which support those options too.