New users get very scared and turned off when the edit something in a WYSIWYG editor, then compare two versions, and see all this strange psuedo programming code with  h2. and *+.  There is no reason a typical user who knows nothing about wiki markup has to see that.  I know Twiki, Jot and other wikis show just the formatted text in diffs, not wiki markup.  Perhaps this can be a seperate tab or checkbox when selecting two version to compare.