iCalendar - appointments in Google calendar (Google Apps)
The iCalendar module integrated smoothly in our project and sending appointments goes without problems. Receiving invitations and processing them with one click works fine in nearly every e-mail client (even Office365!) except for Google mail/Calendar. Our users almost certainly don't like it when they must manually import the .ics file that is attached to the mail you'll receive in Google mail. Although it's a little bit out of the Mendix scope I hope that someone here can provide a (hint for an) solution. EDIT: in a private Gmail environment it works fine.. must be a setting in Google Apps I think.
According to this it depends on the local setting of the user. Not something you can influance. But they do can change it themself with this tool.