I registered at this forum. They emailed me an activation email. In that email was my password. I keep emails. In the event someone sees my old email, they'll see my password.

Two choices:
-- Edit my kept email copy to delete the password and annotate that I did so.
-- Upon activation, change my password, so the password in the email is useless to anyone else.

I chose accordingly. Other folks might like to do likewise when registering with any forum with a similar system.

--
Nick