BuddyPress 1.9.1 is now available. This is a maintenance release, improving compatibility with WordPress 3.8, adding Notifications support for the old bp-default theme, and improves third party Notifications integration. A complete list of closed tickets can be found at the 1.9.1 milestone, and a full changelog is at http://codex.buddypress.org/developer/releases/version-1-9-1/.
This is a recommended update for all installations of BuddyPress 1.5+.
Upgrade via your WordPress Dashboard > Updates. You can also download the latest version at http://wordpress.org/plugins/buddypress.