Dupe is a very handy script if you like to keep track of users. It stores all nicks seen on a host, and let's you easily retrive the nicks.
There's also a function that lets you scan channels for known dupes. This is not a clone scanncer! But be aware that if you use the channel scanner on channels with alot of users you might experience that your mIRC client freezes. So be patient or don't use it.
Tested on 6.35