I run a 10mbit download server using Linux traffic shaping and I couldn't find any way to see how the bandwidth was being shared out to my users, and whether or not people were getting good download speed when my line is maxed out. This tool is exactly what I was looking for and more. :) I was amazed to see it even shows which files they are downloading over HTTP!
pure-ftpd: best thing since sliced bread
The ability to write a custom auth handler is great!! I was able to use a custom handler that talks to my web site API to let users of my website have FTP logins.
Not to mention all the other great features: mysql auth, chroot all but a certain group (admins), bandwidth management, and so on. I think anything you would need in an FTP server you get with pure :)