I came across a problem with this plugin today when my customer was editing a page.
The problem is that TinyMCE is not loading correctly for posts, pages and custom post types because he's not an administrator. (The tool tips is displaying the classname instead of the actual name of the button - see this screenshot http://dl.dropbox.com/u/92436/Sk%C3%A4rmavbild%202011-09-20%20kl.%2011.35.38.png)
I solved i temporarily by changing capability from administrator to add_users at row 161 in the plugin (because his role has that permission).
But the problem seems to be that WP Better Email's TinyMCE is being loaded on non WP Better Email pages.
I am using the swedish version of WordPress, It might have someting to do with that.