Dead Man's Switch is a great implementation of an idea I've thought about a number of times over the past ten years or so.
Basically, it's a failsafe way to create an 'e-mail will'--you write the e-mails you want sent when you pass, they're encrypted and stored, and you have to log in every month to stop those messages being sent. (If you don't log in for 30 days, you get a reminder every week for another 30 days or so.)
I can't remember specifically why I was thinking about this tonight, but I found it with a google search on my Droid while waiting for a very long train...
To be honest, the most frightening idea isn't that I'd die, but rather that there are so many things I feel I've left unsaid--and so many of those things that I don't know if I ever can say.