Review Board 1.5.6 is out the door, packed with some good fixes and a couple small feature additions. Many of these are fixes backported from the in-development 1.6 releases.
Of note are fixes for caching large diffs/files, fixes for screenshot captions on drafts, performance improvements in syntax highlighting (if you haven't installed recently or upgraded Pygments), and support for Fedora Hosted as a hosting service.
See the release notes for the complete list.