Moving from LiveJournal to WordPress & InsaneJournal, and Cross-Posting to All Three Simultaneously
* I was able to copy my LiveJournal archives to WordPress using LJ Archive and WordPress' built-in LiveJournal importer. It copied all entries and comments, although the comments lost their threading. It didn't copy metadata (security settings, icons, tags, moods, music, etc) but I was able to restore most of that pretty easily. (Security settings with a simple MySQL query, tags with the SimpleTags plug in).
* I was able to copy my LiveJournal archives to InsaneJournal using LJ Migrate. It copied everything but comments; moods, tags, music, icons, you name it. I found LJ Sec useful for removing duplicate entries (I'd been manually cross-posting between LJ and IJ for a while.) I found sherlock's tutorials invaluable.
* I installed a bunch of plugins to get my WordPress blog working like a LiveJournal clone (moods, icons, threaded comments with emailed replies, something resembling security settings). Here's a post explaining which plugins I chose. The only thing I haven't figured out is how to get OpenID working with threaded comments, so if anyone knows how to do that, please share.
* There are some areas where WordPress completely kicks LJ's ass. Like excellent statistics, drag-and-drop widgets for arranging your sidebar, tons of nifty themes (over which you have way more control), and awesome plugins for things like photo galleries and managing tags. I was able to duplicate friendslock functionality, but I do miss the ability to post to custom friends groups.
* There's already a plugin to cross-post automatically from WordPress to LiveJournal (or InsaneJournal, or theoretically any other LJ clone site): LiveJournal Crossposter. It's quite nifty, because it doesn't just cross-post new entries; it also allows you to edit and delete entries in WordPress, with the changes reflected on LiveJournal. The only thing it doesn't cross-post is icons, moods, and music, since you need plugins for those. It does cross-post tags, but you have to put them in WordPress as categories (which is easy).
* LiveJournal Crossposter doesn't have the ability to cross-post to multiple journals, though. So I, uh, I figured out a way: InsaneJournal Crossposter. If you install LiveJournal Crossposter and InsaneJournal Crossposter, you'll be able to cross-post to all three sites simultaneously. And you'll be able to edit or delete entries in WordPress, with the changes reflected instantly on all three sites. (Which is nicer than Semagic, because Semagic doesn't let you make simultaneous edits once an entry is posted.) You can also have different friendslock and comment settings for each journal; for example, I've set it to allow comments on my InsaneJournal entries, but not on my LiveJournal entries.
I made this by duplicating LiveJournal Crossposter but changing all the "LiveJournal" references to "InsaneJournal." (I'm kind of shocked that it worked.) In theory, you could also do this for JournalFen or any other LJ clone site, and cross-post to all of them simultaneously.
(I make no guarantees about this, but it's working so far and it's a great time saver.)
If anyone has any questions, I'd be happy to answer. And if you try any of this, I'd be really curious to hear how it worked for you.
Edited to add: I've written up a proper guide on how to migrate from LiveJournal to WordPress. It includes a couple of custom plugins that I modified. You can read it here.