I've been working on upgrading FCKeditor for LiveJournal lately, and just upgraded my development server to their latest beta version, 2.6.3b. Overall I'm fairly happy with the community and development around FCKeditor, but their latest beta release has been giving me a lot of trouble with their Selection and InsertHTML APIs. It is beta, so I guess bugs are to be expected, but these bugs are making this upgrade drag out. This will probably be one of their last big releases before they shift their focus to building version 3, which will probably be a big departure from 2.x.
Today I reported a bug and already the bug has been confirmed and a patch proposed. I'm impressed by the turn around.