For the last months I worked on the PrivateMessaging module. The basic module was already great but my community requested new features, which I implemented. I posted my results to a diffrent [url=http://silverstripe.org/forum-module-forum/show/260103?start=8#post265201%23post265201]thread[/url], but I think they fit better to this forum.
*Added the ability to delete messages
*Added subject and Text to be required fields
*Advanced code comments
*Added instant reply form (function ReplyMessageForm())
*Added status read/new to messages
*the nicknames for the dropdown are processed with htmlentities() to evade an error of the Template-Engine with certain specialchars.