Instead of using taxonomy, it makes more sense to define a custom field that allows the user to access their list of circles. This field would transform any user-targeted flag into a "friend" flag, and any node on which the field is configured into a circles-managed node.
Instead of using taxonomy, it makes more sense to define a custom field that allows the user to access their list of circles. This field would transform any user-targeted flag into a "friend" flag, and any node on which the field is configured into a circles-managed node.