It's generally considered a Bad Idea to do this. You'll have Unix passwords flying over the wire in the clear, making them easy to sniff. Of course, if you allow telnet or unencrypted FTP to the box, there's probably no greater threat anyway, but if you have telnet turned off and ssh turned on for security purposes (like most people do these days), then you've just reintroduced a hole.

-- Randal L. Schwartz, Perl hacker