BuddyPress Activity Stream AtGroups is a BuddyPress plugin by nuprn1 and etivite that will link @(group_slug) syntax to group home page and/or use =(group_slug) to post an update to group.
Plugin homepge: http://etivite.com/wordpress-plugins/buddypress-activity-stream-atgroups/
Requires WordPress Version: PHP 5.2, WordPress 3.2.1, BuddyPress 1.5.1.
Download: http://wordpress.org/extend/plugins/buddypress-activity-stream-atgroups/