It would be cool if this service could monitor your Twitter/Facebook/etc for signs of life to cut down on the link-clicking required, and to add more resilience in the case of spam filtering.
There is a similar service that does monitor your Twitter/Facebook to check for activity. It's http://www.afteridie.org . I haven't really looked into it, though.
I worked on a similar project called seNotable (mentioned by dgunn) that uses public information to determine if the user has passed a way. Seems like there are quite a few of these services.
Might also be nice to have a very simple push notification enabled mobile app for active reminders in addition to passive checks via Twitter. It'll be way less actions from a user's point of view compared to email when on the go.
