You can have a look at the version notes and the News forum for more detail, but here are some of the main points:

Lose
Digests

Gain
Private Messages
Wordlets - enable customisation of wording across the UBB

Changes
"Announcements" replaced by "Forum Intro"
Threads are now CGI-generated, not static HTML pages, but uses new "cache" system
Server load / bandwidth usage has increased
Cookies/Login compulsory for posting

Those are some of the main points, but it's by no means a full list. Suggest you browse the Questions/Feedback and UBB News forums for more.

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