[Thomas Heretic]

Originally Posted by Jolten

It catches all users to the best of my knowledge. If the IP is recorded in the Database then it catches them.

I believe I see the problem. It only catches IPs from the USER table. Since very few posters, from my experience, have static IPs this will not get a complete list of users that are posting from the same IPs.
The problem with an IP search on the POST table is it will not catch duplicate IPs from people that have never posted.
A combination of your mod and the default IP search would catch all users with duplicate IPs.
The screen shots I have attached show an example of the problem with vBulletin's default IP search and your mod. In the screen shots 4 users share IPs but not all 4 show on either method of checking.
Both catch some but not all users with duplicate IPs.