This is cool! Two guys started this site so that you could write an email to yourself and set the date you want to have it mailed back to you, at any specified time up to 30 years in the future.
You could remind yourself of the dreams you once had, as a general memory bank (the contrast of what you now think about your current situation and what you will remember about it in a few years), send yourself birthday greetings, and as a classic exercise for the here and now, of course: where do you see yourself in five years?
Interestingly, you can elect for your email to be private (so that only you can read it) or make it public, and allow anyone to read it in the site after it’s been sent, thus, when you visit the site you can take a look at what other people have been saying to themselves.
source: http://www.mecommshouse.co.uk/ (thanks Jo!!)