With the upgrade, a few features were added, for instance MultiQuoting which I'll be quoting a post from another thread (for the record, no copy and paste was used)
I only use the Fusion (dark) theme, so if you find any issues with any of the themes was have, please post in this thread and I'll be sure to look into it - screenshots help.
Editor Toolbar received some tweaks
Spoiler BB Code
MultiQuote (this is neat!)
Google/Twitter/Facebook Registration (not sure if I'll enable this)
Smiley Management (adding smilies was a PITA!)
A few moderation improvements
Attachment EXIF rotations, basically just rotates the image upright if the image being uploaded has the EXIF data.
I only use the Fusion (dark) theme, so if you find any issues with any of the themes was have, please post in this thread and I'll be sure to look into it - screenshots help.