When importing, iPhoto should use the date and time the photos were taken and your calendar to suggest event names. For days with an all day event (such as a holiday) and time-specific events, the default suggestion should be the more specific event. Overlapping events could be handled by suggesting one and presenting other event titles as options.
Bonus points awarded for allowing embedding of location data (XMP address, city, state/province, ZIP fields) if present in the calendar event’s location field. This embedding would probably be off by default for privacy reasons.