Rated 5 out of 5 stars
Awesome, I've been wanting this exact thing for some time. In outlook I had to make due with their "follow up" flags and making notes there, but they were more limited in how much I could write. This leaves more room for notes. The only improvements I can think of are the ability to leave more than one note on an e-mail. If I have a note stuck to one now and click the XNote button again it just goes to the note I've already got posted. Also, it'd be cool if the note actually "stuck", so that when you scroll the note scrolls with the e-mail.
These are both minor quibbles, and am delighted to have this add-on in it's current form.