If you are browsing LiveJournal being logged in to your account, be warned – there is a way for LiveJournal users to see who read their posts. This functionality is currently available only to Russian users (yes, related to recent SUP acquisition of LiveJournal) and is provided via LJ.ru service.
There seems to be no way to opt out of being seen by post authors, other than using a separate account or browsing LiveJournal anonymously. Both of these ways have their limitations though (access, comments, friends, etc).