It has already been brought to my attention twice that there are people and organizations who are not happy about this problem, so I hope this doesn't sound too paranoid, but I think it would be a good idea for all of us to make occasional local backups of the data. I'm trying to do it every day, but I would be happy to know that someone else is also backing up occasionally.
From what I understand, if you use the Zotero Standalone (I'm new to this and have never used the Firefox add-on), the program will automatically sync, and backup, every few minutes. If this doesn't happen for you, then check the options and preferences under the sync tab. I have over 1.4 gig of 6000+ entries in this project backed up on my local drive!
Thank you everyone invovled in this project. I actually started my own group in Temple University for shared Buddhist studies bibliographies a few weeks ago before I found this great resource.
Yes, of course Zotero syncs everything locally automatically--and not only in the standalone version. But this means to me that it would not be inconceivable for someone to go in and delete a bunch of stuff, and that these deletions would be synced to your local system before you were aware of it. I save outputs in Zotero RDF format every couple of weeks, so I guess it's not necessary for everyone to do it.