I was converted by my partner.

We do use it extensively at home. We our own web-based app, and just about everything gets entered as a task and delegated. Or sometimes set up as a shared project we can both access and work from, depending on what the project is.

We also don't expect the other person to act on anything unless it's been written down or typed into the system. With extended family that aren't GTD-ers, I either ask if they can hold on a second so I can grab a pen and capture something or ask them to send me email so I can forward any follow up into my system.

With both of us at home using GTD, I'm really happy with the effect it's had. It means we spend time together talking about things that aren't just the administrative overhead of living as a couple. It also does a great job of eliminating the subtle irritations of "I asked you to help you x and you forgot".

For paper mail we pretty much just grab it, pull out whatever one of us needs to deal with, and pass off the other stuff to the inbox of the other person.

It's pervasive enough in our shared life that while I was in the middle of something else yesterday and needed to capture an action as I thought of it, so I resorted to "do you have your phone? Could you please Jott me to send the info on jP's to my friend for her happy hour?" Which, I realize, may be a bit dorkier than what most people's significant others would find normal...