It appears that Livejournal is currently suspending communities for abuse of livejournal tags. The limit number of tags a community can have is 500. Any more than that, and you risk having your community suspended until you cut down on the number of tags. So, if you've got a thousand members, and each one has their own tag, then they're likely going to catch you. I've had two communities I belong to in the last few days suspended for having over 500 tags.
Off-hand, I would say that this is most likely to affect fanfic challenge comms.
Please feel free to pass this on.