OK...I assume it wasn't really "random" but I sure can't tell what happened.
This is basically the situation: We've installed 3.0 (recently upgraded to 3.0.1) and created Networks. We also installed several plug-ins. As of last night, we had Google Analyticator, List Authors, Stream Video Player, wpCas, WP Multi-Network (with two additional networks set up), and the New Blog Defaults plugins, with the New Blog Defaults and Stream Video Player being installed yesterday afternoon.
Well, when we came in this morning, we found 3 things have changed since we left the server last night (that we've been able to find so far):
1) One user who had been an admin over a test blog, where he was playing with stuff (we're still in development mode with this software) found that he was no longer the admin of that blog (he wasn't even a user of it)
2) I had added several users to a blog before, but had to delete it and re-create it later. I had never re-added those users to that blog. Yet this morning, they were all listed as users of that blog as subscribers (which is odd because I had added them as editors before)
3) I found that that same blog, if you tried to access any page on it, just redirected back to the wp-admin for that blog. (I can't see anything in .htaccess that would cause this)
This blog isn't accessible outside of our internal network, and there is no evidence that anyone inside the network accessed any of the admin pages overnight. The only thing we saw was one person's computer repeatedly accessing the comments RSS feed overnight (which we thought was a little weird, but shouldn't cause any problems) and wp-cron.php running a couple times.
I've disabled all of the plugins except the Multi-Network and wpcas for now, but none of the issues have been resolved, and at this point I'm at a total loss as to what might have happened overnight to cause these things occurring. It would be nice to figure out since if there is a security problem that's causing this, we'd definitely like to know.
If it's a problem with one of the plug-ins we installed, or plugins not playing nice, it might be nice to know as well, but at this point, I'm looking for anything that might have caused this odd behavior.