This evaluation contains some interesting points about WYSIWYG editors and some common mistakes. It might be a good idea to keep those in mind, eg:
[quote]
* Remove toolbar buttons for rarely used markup items such as justified text (justified text on the web is bad for readability).
* The default installation should provide buttons or menu options for inline quotes, blockquotes and acronyms.
* When creating a table, headers should be created by default instead of forcing the user to add them later. Throw in a default caption as well to make sure content editors do the right thing.
* Make sure images without alt-text specified receives an empty alt attribute.
* Do not use the icon for “indent leftâ€