Lots of bugfixes, and some feature and performance enhancements.
A new EDIT_TOOLBAR from mediawiki, more page permission enhancements,
reduced memory usage for pagelists which need no page content,
related improvement for OldMarkup crashes because of PCRE memory exhaustion.%%%
New <!plugin-list !> syntax and PhpWiki:PageListLibrary args.%%%
Because of SQL changes you'd need to ?action=upgrade to update for SQL.
for the download link and detailed (unfortunately unformated) release notes.