dpolicar and I were discussing blog comment rating systems when the subject of LJ's blog rating system came up. Your number isn't displayed unless you've opted in to cyrillic services, but they do rate all active LJ accounts.
Social Capital is intended to identify how active and influential a user or community is. Each account's Social Capital is based on many different criteria, including the number of users who have added the journal or community to their Friends list, and various other activity throughout the site: how old and active the account is, do they leave comments in other journals and communities, how often do they log in, and many other factors that differentiate real users from bot accounts.Interesting, though I don't know that it's used for rating comments. Yet another cyrillic services feature that makes me pleased I opted in.
Social Capital is calculated for all LiveJournal users, with the exception of empty or inactive journals, and suspected bot accounts; these are not included in Social Capital calculations and do not increase the rating of any user or community.