In my setup WordPress 3.0 / latest Buddypress / Cosmicbuddy theme an error occurred in showing individual groups:
BP_Group_Extension::widget_display() must be over-ridden in a sub-class.
Added in bp-maps-groups-maps.php the empty function widget_display() and error solved...
The BP_Group_Extension API requires this function to be overridden in the subclass. Please use this in next version.