As stolen from telophase as she says and links it as well or better than I could. And I hadn't actually seen a notice 'til I checked my flist. Sooo... in case this catches even a single person, I'll be happy I did it...
Tomorrow, LJ is doing amassive server moveand will be offline for four hours (possibly less, possibly more), starting 11 AM EST/8 AM PST. They're also bringing it up slowly, rather than all at once, so it may take a while for all functions to be enabled.
More on this at the link above.
Today might be a good time to back up your LJ:LJ-Archiveand other options are out there.