BuddyPress now integrates more elegantly than ever before with your WordPress theme, and there are improved tools for theme developers and designers to tweak (or completely overhaul) the way BP looks.
A slick unit testing framework and integration with Travis CI, which developers can leverage when working on their own plugins, themes, and even client sites.
Big under-the-hood improvements to the Groups component, making it easier to develop plugins and easier to scale.
You'll also get a sneak peak at what's coming up for BuddyPress 1.9, already in development.