I could be wrong but I don't think it grabs two users with one IP. It uses the cookies that the forum sets. When it read's the cookies on login, it tags the discrepancy between the logged in info and the cookied info.
If you had two people using the same computer (say at work) it would keep showing the user as the same person even if one logs off and the other logs in.
Works great in my opinion.
Please correct if wrong...
