BlackBerry Messenger 6.0 leaked and available now for devices running BB OS 6
BBM 6.0 brings with it integration with Twitter among other social networks, plus the ability to chat with contacts while playing a game, and enhanced file sharing.
While this leak appears to have come from RIM, you're on your own if something goes wrong. So best make sure you have a solid backup before trying anything. Head on over to the BBH-Plus forums for more information.