I have tried just about every calendar system out there over the last twenty years - Daytimer, Palm, family notebook, Outlook. When keeping track of my own calendar, I could usually make things work pretty well, but keeping track of multiple calendars (mine and Mr. Math Tutor's) has given me fits. How could we each have calendars that kept up with events that would affect both of us? If I used a paper calendar, I had to add to it regularly and generally missed things. Electronics are ideal, but it's hard to coordinate both my and Mr. Math Tutor's schedules. We have, though come up with something that seems to work - Google Calendar.
Here's how we make it work for us: Mr. Math Tutor set up his own Google Calendar then gave me permission (in Google) to add to his calendar from my Google account. When I am in iGoogle (which I usually am), I can see this calendar which contains all family events. Mr. Math Tutor just got a Blackberry which he can sync directly with Google Calendar. We have the Google Calendar set up to automatically sync with Outlook. I use a Palm and HotSync with Outlook every couple of days. So far, this works for us. It was a little effort in the setup, but is pretty easy to keep up with. Now, we can see where the other person is and what they're up to!