When scheduling meetings, the participants have the option of being
scheduled as Required, Optional, or Non-Participant.  Yet when they
receive the meeting invitation (in their Evolution), they don't have the
option of the meeting being free or busy; just Accepting, Tentative, or
Decline.  I think that Accept and Tentative should both have options for
the time being free or busy.  Furthermore, if the invitation was sent to
a Required Participant the default for the recipient should be
Accept/Busy.  If the meeting was sent to a Non-participant, the default
for the recipient should be Accept/Free.