WSJ.com (soon to be part of Murdoch's empire) had a story on the troubles of married couples sharing technology: 'Til Tech Do Us Part. (Subscription?)
The story highlighted the problems created with a shared music library, recording on Tivo, joint email accounts, NetFlix, Amazon.com recommendations, and joint blogs. A jogger is jarred by having his wife's music popping up while he is running (I guess he never heard of a playlist). I was the most surprised at the joint email accounts. Google, Yahoo and Hotmail have offered free email accounts for years. There is no need for a joint email account.
I think most of the problems in the story are easily solvable, but it does raise the issue of the impact of personalization. It is great having your experience customized to you, but some services need to better distinguish when something is for you and when it is for someone else. Amazon.com is the best example. I am not sure why gifts for others impact the recommendations for me.
The bigger challenge in my family is not parsing joint accounts but combining multiple accounts. My wife has her own email accounts, online calendar and contacts. Some of that information needs to be shared with me.
We seem to have solved the calendar issue, by using Google calendars and giving each other access. On my Google calendar account, I can pull up her Google calendar and see her information alongside my information.
Email is not really a problem, because it is easy enough to forward a received message or cc each other on outgoing message.
Contacts is our biggest problem. For example, she has the phone numbers for the babysitters in her contact list. I have not figured out how to solve this problem.