From Boing Boing comes a post about a website, futureme.org, which lets you send an email to yourself (or conceivably, someone else) in the future. Here is the email I sent:
Dear FutureMe,Worried about the privacy implications of this website, but I guess you would know better. Are you still paranoid about privacy? I hope so. Can't wait till PastMe.org comes about! Anyway, lots of love, and here's hoping you have a flying car.