If you allow Guest users to create Kablink Vibe accounts for themselves, as described in Section 5.4, Allowing Guest Access to Your Vibe Site, you might want to delete accounts that are inactive for a period of time. You can use the Login report, described in Section 23.2.1, Login Report to generate a list of users sorted by their last login date. This report does not include users who have never logged in, but presumably, if a user self-registers, the intent is to log in immediately.