I want to start off by saying I am a fan of this plugin. I was using version 0.2, and tried upgrading today. It was a bit rocky, but I got things working.
I had to create wp-includes/js/tinymce/themes/advanced/skins/wp_theme directory and copy the content from wp-includes/js/tinymce/themes/advances/skins/default to get the plugin to work properly when I clicked "Activate".
However, I still get a 404 loading wordpress.css from a different location, because that file does not exist. No big deal. The plugin still works.
The suggestions that I have revolve around keeping the output consistent with older versions. For example:
0.2: The class on the LI tag was rtw_widget
1.X: The class on the LI tag is widget_richtext
0.2: The content of the widget was wrapped in a DIV tag
1.X: The content is no longer wrapped in the div.
Both of these changes have broken my CSS. I have updated it, but I feel that you can have all the improvements without changing the fundamental output.
Also, of note but not important, the ID of the outer LI element is now 'richetext-#' as opposed to 'richtext-#'. I assume this is a typo. Didn't affect me, but might someone else.
I am going to jump into the code for this and see if I can change the output routines to make them consistent.
But, again, thanks for making this.