(maybe download your facebook data before, get phonenumbers, emails etc. cause your facebook will be GONE)

first you need a random string you shouldn’t be able to retrieve
like this one:
H9qth1vTaWYACuMlc2KL
You shouldn’t use this one cause you’ll be able to retrieve it.

go to http://www.random.org
and make your own, paste it in a notepad file, DONT SAVE IT!

now go to hushmail, create a new account, and use the random string as your password.

Remove your old emailadres from facebook and add the hushmail address instead.

Remove any phone associations.

Validate the hushmail account for facebook.

Change your facebook password to the same random string.

Delete your facebook account.

Remove the random string from notepad.

close notepad.

It is now Impossible to retrieve your facebook account.

Why would you want to do that? I have friends who stopped facebooking, and I kind of lost contact with them. Is in not possible/better just to reduce time spend there?