Better safe than sorry...

http://syredronning.livejournal.com/1530901.html has a link to a fixed version of LJArchive. I have heard from many people that it now works fine, both syncing entires and comments. I will be using it when I get home.

If you download it, be sure to thank the journal owner syredronning, who paid a coder to fix it.

...and back up your data. Always. Often. Twice even. :)

UPDATE: Tried it - worked fine for me. Your mileage may vary...