Events

• It would be great if I could mark an event as "canceled". 
• Create a "link" between G. Calendar and G. Maps for the "location" field so one could use his own G. Maps "Saved locations"
• Able to 'shadow' events from another calendar onto your main calendar, so as to receive email/text notifications, either 'shadow' all events, or specific events.
• Event templates (user creatable) so that an event can be created quickly with, for example, a pre-set notification periods, and a pre-set calendar, eg my own Birthday template would have notification period of 1 week and create the event in my Birthdays calendar.. At the moment I have to manually edit every event to change the notification period.
• Make Event Date relative to another Event date!  If I have an Inspection report due within 3 days of the inspection, and remedies due 7 days from then, all three events are linked, and based on the Inspection Date.  If the Inspection date moves 1 day prior, so do the report and remedy dates.
• It would be great to be able to say an event comes, let's say, on the 1st and 3rd month of everyday.
• Delete some instances of repetitive events, like delete instances for holidays.
• Calculate the number of days between 2 events.
• http://iancamarillo3.blogspot.com/2007/04/updatedynamic-notification-by-ian.html
  
• Ability to give a starting date, e. g. for an event "my birthday": 07.02.1974. Then, in following repeating occurrences the time difference could be stated like "my birthday (33 years)".
• It would be great to see if the event is busy or free for user without checking details of the event.
  

Export

• Export Calendars

Reply 

•  Often I need to reply to the person who created the calendar event with an email to ask if they are coming, to ask what the room number is, to ask what the conf call numbers are, to ask if they are coming, to ask for pre-meeting materials, etc.   There are many reasons to need to reply to a calendar request with an email.  I used this feature of Outlook nearly every day and miss it greatly in Google Calendar.
  

Import Events

• Import Events using plain-text or xml files (so that you can upload many events with just a file, not one by one). Something like:

<event>

    <event-name>My birthday</event-name>

    <begin-day>29</end-day>

    <begin-month>2</end-month>

    <begin-year>1976</end-year>

    <endday>29</end-day>

    <end-month>2</end-month>

    <end-year>1976</end-year>

</event>

User Interface

• Mimic Google Maps interface - for example, a single day would look like it does now, but you could grab anywhere on that day to move it up or down for more times or side-to-side for previous and following days. Additionally, you would be able to "zoom" out to view more days or a few weeks or months or even years.
• View Calendar by Year
  
• Word Wrap when using the the Monthly view. 
• Built-in week numbering (like http://recover89.googlepages.com/googlecalendarweeknumbers does)
• Pop-up event detail when hovering over event.  

Reminders 

• Create multiple reminders for one event.  It's nice to be reminded a day before and perhaps an hour before.
• Actually receive reminders from other calendars. Otherwise, not as useful.
• http://iancamarillo3.blogspot.com/2007/04/updatedynamic-notification-by-ian.html
• Have task and TODO notes available.  These should be somewhat like "Remember The Milk" and Outlook, except they would be color coded per the calendars and have an active popup option on the day so you will see your list when you first access your calendar.  "Remember The Milk" is OK, but doesn't integrate enough into the Google interface.
  

Sync

• Sync with applications like Microsoft Outlook, Lotus Notes and ACT! with one click rather than Export and Import - like Yahoo Calendar does using Intellisync - but add the facility to sync automatically at set times 
• Sync with Mac OS X iSync 
• Sync with any mobile device with www.mobilegcal.com for free.  Check out the demo at mobilegcal.com.

Project Management 

• Use Google Calender as a project management tool such as http://www.activecollab.com/
• See Event Date relative to another Event Date, above