WARNING: If this LJ posting makes absolutely no sense whatsoever, there is a really good reason. As I type this message, I am listening to the 62-hour-long MIDI of my entire LiveJournal contents. And honestly... I cannot take this seriously. At all. XD
For those of you concerned about LJ and its relative longevity, I promised some friends that I would try out some LJ archiving software, and try it out I have. My first Google hit (not to mention a program referenced by someone else) is called
ljArchive. The software seems to be relatively robust. And... honestly, it's rather fully functional. To download my whopping total of 288 entries over the past six years, it took less than a minute, comments to my journal entries included. And it saves them in a nice custom format which you save onto your hard drive, which will pull up all your journal's contents within the application.
It supports multiple journals (for those of you with Multiple Personality Syndrome... or with RP journals) as well as communities (which is important for those of you who REALLY want communities backed up, however note that to download a community's comments, you need moderator access). It will automatically sync up with your journal to get new content should you archive stuff now and then add entries later. And it gives you a nice convenient database of all your entries (and all the comments applied to your entries). As far as export abilities, it will export to HTML, XML, and (as aforementioned) MIDI (lol). It can search your entries for specific searchable words not to mention perform all sorts of statistics and analysis on your journal, such as who comments on your journal the most, what words you use most often, and your emotional profile in comparison to other LJ users. It will even read your entries back to you. (I apparently didn't have this set up though, so I haven't actually tried it out. Not that I really WANT to be able to hear my entries aloud. Shudder!)
The only question remains how easy it would be to re-upload this sort of stuff to another journal-like thing, though my hunch is that such a task would be relatively difficult in general since I doubt there are many cross-journal pieces of software out there on the market.
At any rate, if nothing else, I recommend this one.