We've done it for a while and it works well for us. We're both busy people, and parents of small children.

1. We each have an iCal calendar, and we each subscribe to each other's calendar. Yes, there is sometimes duplication; we live with that. Because I don't always have web access, I didn't want a web app for calendaring. They're all still too slow. I'm anxiously looking forward to Leopard's iCal shared-calendar enhancements, however.

2. We have a scheduled, weekly "family business meeting" where we review calendar items, @waiting for items, and other family business. We keep an agenda which we review weekly ("Last week you said you'd work on XYZ. How did that go?"). We keep notes of our meetings, too.

3. We each have an inbox at home, which we use to pass stuff to each other. We use our inboxes quite a bit.

4. We also pass a lot of info via email. Even if we're in the same room, I'll send my wife an email reminder about something she said, or about an idea. She'll even ask, "I need to buy more shampoo. Would you send me an email about it?"

And that's it. Beyond those points, we each run our own GTD system. We're pretty vanilla in our implementation. I think we got a lot from David Allen's description of how he and his wife work together on the Getting Things Done FAST series.

Good luck.