Long awaited really. With the new Social menu offering profile, group, and custom avatar functionality. Plus, platform chat features that are now expanding to the new Blizzard Groups which can have multiple text or voice participants, with Group history saved so if you're late to the party you can catch up on what's happened so far. Probably not much though.
Also new in the update to Battle.net is the ability to gift items to players, like Hearthstone card packs. Thanks press release.
The new profiles can be made private or public, and best of all you can now appear "offline". A feature requested by a large number of people looking to avoid social interaction online.