I played with FCKeditor in my development site and after various configuration changes it stopped showing. It took me a while to understand what has happened. I've seen some other issues that might be related (e.g. http://drupal.org/node/190010#comment-777573 ). I'm not sure I understand all ramifications so feedback is appreciated. If my analysis is correct I suggest to document this behavior, possibly in http://drupal.fckeditor.net/troubleshooting.
FCKeditor will show on your textarea if both the conditions specified on the profile you assigned AND the global profile match. The 'local' profile does not override the global profile in this respect. The help text does says "It is possible also to define the Global Profile that will hold values that will be appended to all other profiles." But it wasn't enough for me to understand what it actually means.
In my case I set the default profile to be associated with all roles. I configured the inclusion/exclusion mode in the visibility section to 'include' and set 'edit-body' in the list of fields. What I did wrong was (this was done much earlier on) was to change this mode to include also in the global profile, but without updating 'edit-body' there. What happens is that FCKeditor matched edit-body in the default profile, but didn't show as it didn't match the global profile.
You can check this in code: line 867 in fckeditor_process_textarea in fckeditor.module, $enabled is checked against the global profile after it has already been checked against the local profile.