Edited feeds will no longer be reposted. Rather, the post itself will be edited. This change will most affect feeds like wilwheaton, where the author commonly edits his page. This change will only work for feeds which have "good" link format - I'm not sure exactly what this means, but it seems like if the link to the post has a number on the end which increases or changes steadily, these links will be searched first. If a matching link is found, the post will be edited.
Additionally, note that only posts up to two weeks old are stored on the LiveJournal servers for syndication feeds. These posts are then deleted (since they won't be showing up on any friends page views anymore). Therefore, any post older than 2 weeks old will be reposted instead of being edited. Also, it only works on items which were added after the code went live, 2 days ago.
Edit: alicetttlg has confirmed that this code is live. Changlog post is available at http://www.livejournal.com/talkpost.bml?journal=changelog&itemid=424022 .