My wife and I both have reasonably busy schedules, but we never had a way to keep track of each other's schedules. We've both carried PDAs for a long time and maintained our schedules electronically, but we still didn't have an easy way to view or edit each other's schedule.
As part of a larger shift (which is the subject of a future post), I moved both of our calenders to Google Calender. We still use our PDAs (Palm/Treo), but we use Companion Link's synchronization tool to keep them in sync with the Google Calendar. Using Google Calendar we can view each other's schedules, and easily copy appointments from one to another.
Google Calendar also allows you to view other public calendar's on your calendar as well. I use the US Public Holiday's calendar, the Illini basketball schedule (although this year I wish I didn't), and the Chicago Bear's schedule (much more fun to watch this year). You can turn on or off any calendar, so it doesn't clutter up your views.
I don't sync the other calender's with my Treo, so it is maintained as my clean primary schedule.
It has been a great solution for us, and while it isn't perfect, is a very good low maintenance approach.