Having running statistics on your systems is always a good idea.
Since I am a qmail freak, I have been using the venerable qmailmrtg7 for a long while.
In fact since I use my courier pop3/imap server with tcpserver, I can even use qmailmrtg7 to give me stats about POP3 and IMAP, which it susually doesn't.
But... qmailmrtg7 is kinda lame. In part it is lame because it uses mrtg. In part it is lame because it's one opaque thing.
So, why not make a qmunin based on qmrtg which will marry them?
Well, that's an idea.
It's not even very hard to do :-) I should probably do it and publish it.