For years I've been using (occasionally, when necessary) a small custom routine that inputs an IP address (or part) and reports all usernames that have used that IP address (based on TblThread).
This is useful when an admin/moderator wants to check if a posting might have been made by someone who has multiple usernames (and probably up to no good!).
I know it's not an exact science as IP addresses change, however it helps me a lot and the part-IP address also helps in some circumstances.
I just came to wonder if a simple pop-up that does this would be a useful standard feature in WWF. I imagine a button wherever an IP address displays, just like the existing IP Information button.
It would be great to be able to check where else in the forum an IP address had been used !