I made my first plugin for roundcube 0.3 stable, passwordext.
You can download it from here:
Downloads - roundcubeplugins - Project Hosting on Google CodeObviously, based on original password plugin by Aleksander 'A.L.E.C' Machniak.
Current improvements: supports certain password strength checks (min length, alpha, digits, wrong copy/paste protection, username and domain not part of password). Check README for more details.
ToDos: force user to change password based on certain criteria.
Please report issues/request for improvements on the Google Code issue list.
Have fun with it.
P.S.
Translations are welcomed.