It looks like “Tumblr envy” is spreading throughout the blogosphere as LiveJournal has joined WordPress (not to mention Typepad as well) in copying a feature that has set apart Tumblr from the rest of its rivals.
You can add a repost button that allows other users to share all or part of your entries on LiveJournal. Please note that you must disable auto-formatting to insert a repost button. This button is only intended for public entries (i.e., if your entry is marked friends-only and you add the repost button, the entry can be reposted publicly by others, although the original post will remain friends-only). (Official LiveJournal Blog)
Unlike WordPress (who forced this feature upon the WP.com universe), LiveJournal requires users to manually insert a piece of code in order to activate this feature upon their LJ blogs.
While inserting the code manually makes the repost button “user unfriendly,” it may also help curb down “reblog spam” (as only geeks seeking traffic will proudly display this button).
Hopefully the LiveJournal team will consider making the repost button user friendly in the future for non geeks, as well as “opt in” (as not everyone wants their posts reblogged to the masses).