It amazes me how many sites allow you to register, and then send you an e-mail to your registered address containing your password in plain-text. There is never a warning stating that the site will email the password you use, for all to see.
Sending passwords by e-mail works when you forget a password. The site changes it and e-mails you the new one, which you then use to log in and change it to something else. The e-mailed password is not active for very long, and it isnt something you chose.
Sending you your own password, either in a welcome e-mail once you register, or as a response to a forgot password request is bad security. Really bad security.
You cant tell whether a site is going to do to this, so it isnt possible to use a less sensitive password for sites which will e-mail your password back to you. If you have groups of passwords; one for sites...