This idea already exists in the Luminate idea bank and I think it should be in the BBIS/BBNC idea bank as well so I am re-posting it here.
"It would be great to have a feature that allows people to add the event that they signed up for to their calendar. One way this could be accomplished is by allowing Admins to upload .ics files in the document library. A step beyond that even is for this file to automatically be generated if the Admin selects for that. I understand there may be limits to the number of files we can save so allowing Admins to choose only the most important to have the .ics file. Another option would be for files to automatically terminate after the event start time. (Or even RSVP deadline)"
I am aware that some of this functionality exists using the Event Calendar part, but it is not fully developed. The Outlook option sends the user to a Windows Live login screen, it does not generate an .ics. This is very much a feature that most users expect to see when they register for an event online.