Look , my answer is related to web programming just a bit. In Registration progress, when the engine gots your wanted information such as : user name - password - email address and more, it will begin 2 process. at first it makes an MD5 copy of your desired password and insert it to database, then it set a plain text copy of that to your mail box using mail() function. So your passwords are still secure unless there is any problem due to your mail account security.
Tips ::
1- if you pay attention you will find out that on retrieving password using "Remember password" in (PHPBB), it makes a new copy of password for you randomly, if it was plain text in database there was no need to make a new one !
2- if there is a problem in your mail box there is nothing safe for you , ANYONE can hack you through this link ::
ucp.php?mode=sendpassword
3- this is just first my post , congratulation ...
There is just hope to got it ... TRY ... !!