If I send you an email, it doesn’t matter whether I am using Outlook, Gmail, Thunderbird… You can read it, reply, forward, delete etc. with your own email program of choice. But for calendar users there is no such luxury of cross-platform calendar interaction. We can send calendar invitations to each other in some circumstances e.g. a Google Calendar user can send an invitation to an Outlook user and it will be interpreted correctly by Outlook.
However, calendar sharing between different calendar programs is difficult, impossible or expensive. If you’re using Outlook without an Exchange server, how do you share your calendar with a friend on Outlook, Apple iCal or Google? The lack of standards in calendaring makes this a daunting task. The only workable approach is to get the people you need to share with to all adopt the same calendar program, assuming that program has sharing which not all do. This is not really a solution to my mind.
There are some point-to-point solutions that let you keep two of your calendars in sync, e.g. Outlook and Google, but I think this is only a small part of the solution.
If we could provide a cross-platform calendar sharing solution, would people find it useful? I certainly would find it useful to let my wife on Outlook Calendar have access to my work Google Apps calendar and vice versa. What sharing permutations would be the most beneficial? Outlook <-> Outlook or Outlook <-> Apple iCal <-> Outlook or <-> Google or Google <-> 30boxes.
Sharing is good, let’s make it accessible and easy!