IF the feature list could be released we would be able to tell you whether new things are added properly, or are having problems
(also, will PR2 themes be compatible with PR3? Official Release?
The theming system has some bugs in it atm. I wouldn't think it would affect current PR2 themes though since they are mostly export/import and extra css ones.
As for the feature list, heres a short list I created ages ago. Its not 100% complete, so if you find one thats not there, please tell me. I'll add it for annoucement for the final release.
New Features
Front End (forum)- Publicly joinable usergroups (group memberships)
- Brand new Archive/Lo-fi system
- Ability to save Post Drafts
- Manage Attachments page
- Accumulative attachment size limit
- Forum rules per forum
- Ban Reason for Banned forum members
- Email notification of new Private Messages
- Custom Usertitles for allowed usergroups
- Avatar size limits set in pixels (WxH)
Back End (admin cp)- Plugin manager page (to activate/deactive plugins)
- Multiple Usergroups per forum user
- Disable new registrations
Scripting (php files)- Registry Implementation to enhance myBB security
- Plugin Implementation (hooks) for mod makers
Changes/Updates
Front End (forum)- A brand new default theme
- Avatars is now Avatar Galleries with Default and Assorted Avatars
- Forum categories split on index.php
- Search-bots listed on Online.php
Back End (admin cp)- A themes system with far better customization
- A brand new templates system with easier navigation
- A brand new help system
Scripting (php files)- Option to have cache in files rather than in the DB.
- Avatars and Attachments are now file-based
- An improved, fully translatable language system
Requirements- PHP 4.1.0 or higher with XML support
- mySQL 3 or higher
Those are just the major changes though. There are other smaller changes that weren't documented here.