As suggested by MonoX team,

copying here my comments/suggestions from

http://www.mono-software.com/Mono/Pages/Discussion/dtopic/mMWDW1Tw7kCBuaOaAT_4ZQ/user-activity-stream-for-friends-only/?dmsgId=vjXsiUjk40K8H6OeAaP4hA#PostvjXsiUjk40K8H6OeAaP4hA
</br>
</br>In communities with many users, the activity stream becomes just noise if you can't filter it to show activity from your friends only. The default should be that btw, and optionally be able to see all activity.
</br>
</br>Moreover, social networks like Facebook don't show all activity also for privacy reasons (there are people who don't want their activity shown everywhere) I guess, but only show you friends' activity

...regarding my privacy comments above, obviously admins should always have option to see all activity (and also moderators should be able to do this in their groups)
</br>

...speaking of groups, taking part in a group should automatically list you to see all its activity (actions of its other members that affect the group resources though) I guess