XWiki Enterprise 3.1 Release Candidate 1 was a bug fix and stability version only and as such there are no new features.

You can review the bugs fixed since 3.1 Milestone 2 by going to:
http://www.xwiki.org/xwiki/bin/view/ReleaseNotes/ReleaseNotesXWikiEnterprise31RC1

And download the new version:
http://www.xwiki.org/xwiki/bin/view/Main/Download