Here's the super-simple test page I've been having people check: http://scripts.webmastersite.net/test/cktest8.html
The behavior in these failed cases is that it hides the textarea but doesn't put anything in its place.
One affected user reports: "when I use Chrome's developer tools, the textarea has a visibility attribute of "hidden". If I remove the <script...></script> tags, it shows up fine. My conclusion is that something in /ckeditor/ckeditor.js is setting the visibility to hidden on page load. I've tried removing this on test8 (and the earlier tests, hoping that the ckeditor will show), but it simply reshows the original textarea with "<p></p>" as content."
Note that the real problem isn't so much the hiding of the textarea (though that makes the brokenness that much more broken), it's the fact that the ckeditor doesn't load.
Anyone have any ideas? This is with CKEditor 3.4 now, but also affected 3.3.2 for sure, possibly earlier versions.