We enabled FCKeditor on our Wiki and it has caused a few problems with loss of page formatting if someone opens the page with the editor enabled. The most frequent problem is the use of leading spaces to put indented text into shaded boxes, or any kind of text indenting. That gets messed up when the page is edited with the editor enabled. Usually that can be fixed by reverting to the previous version and then editing the page with the editor disabled. We suggest to our users that they disable the editor as a default if they are editing previously created pages, and only enable it for new pages where they want to do things such as complex tables that are much easier using the editor.
PatW