I've already posted some feedback in the Administrators forum on our small test environment.
This is more from a user perspective reported back to me. Hope it hasn't already been posted (I did a search).
When composing in plain text (our default), if the user decides the change to HTML, anything already typed is wiped without warning.
A user found this the hard way after typing a very lenghthy message only to have in nuked when she decided to insert some bullet points (by switching to HTML compose)