I frequently find myself finding out about appointments of various sorts
from mail messages sent to me (they are typically not in a form
conductive to automatic updating of the calendar). Often, there are a
good deal of details regarding the appointment in the mail message that
I would like to have as a part of the appointment details (things like
'where', 'why' and 'how' come to mind).

With that in mind, I'd like to have another mail action (something like
"Add to Calendar") that would give me the appointment editor, with the
text of the mail message already entered into the appointment
description. Yes, I'd have to give it a summary and a time, but then,
I'd have to do that anyway.

Having this functionality, I no longer have to be worried that I
accidentally delete crucial information from a mailbox before the
appointment has passed.