Now that I'm about to leave work, I've been forwarding all sorts of calendar events from Outlook at work to my personal e-mail account as a reminder to place the events into iCal on my Mac at home.
I forwarded one event from Outlook 2003 to my home e-mail account, and I was surprised to open the e-mail and find that it asked if I wanted to place the event on my iCal calendar. Outlook 2003 and iCal speak the same meeting language! I was surprised, in a pleasant way.