Fully customizable portal and side columns. Ability to turn columns on/off and move column boxes around. The portal utilizes alot of caching to keep things fast.
10 fully customizable portal boxes. These can contain php code, can be cached for a certain amount of time, or be a static file for things like Google's Adsense. The flexibility of the custom boxes will allow users to pull all sorts of data from the forums, trade portal boxes with other users, etc.
The portal boxes, including the customized ones, can be used on other pages outside of UBB.threads if they are php enabled.
Much easier RSS syndication. Options to create the RSS feed while editing a forum. Forums that are RSS enabled have the proper RSS headers sent to the browsers. Ability to make RSS feeds that span multiple forums as well.
New ActiveText feature. This allows you to translate certain keywords into links or images when the posts are being displayed rather than entered into the database. This allows you the flexibility to turn this feature on and off as needed. A variety of ways this can be used to empower your site.
Ability to watch topics, users and forums, with options to be notified via email when a new post is made that matches your Watch Lists. The old subscription model that required a cronjob to be setup has been removed. In fact you no longer need to setup cron for any of the features to work.
Unlimited levels of subforums.
Full Text indexing on search data.
Option to allow one of the custom portal boxes to be placed between the 1st and 2nd post of individual forums. This is normally the best place to put ads.
Private messages have become Private Topics so the whole history of the conversation can be viewed.
Ability to lock profiles to only be viewable by registered users.
File attachments can be turned on/off on a per forum basis.
Polls can be turned on/off on a per forum basis.
Allowing polls in replies or only in topic can be turned on/off on a per forum basis.
All User IPs visible to admin on the who's online screen.
Ability to lock forum into flat or threaded mode.
Front end templates rewritten to now use the php Smarty template engine.
Moderator option to receive notification of new posts when a post is made in a fully moderated forum.
Better ability for moderators to approve posts and manage members when they have the permission to do so. This utilizes the control panel to make the moderators job much easier than the prior method.
Toss in Smarty templates, mix with a healthy dose of Ajax and you've got yerself forum software second to none.