Stop notifications on Activity comments
Currently, if you comment on an activity you will receive a notification for every subsequent comment on that activity by anyone else. As you can imagine this can get pretty boring. For example, Niki Terpstra's famous Paris-Roubaix Strava upload has 542 comments to date, so the first commenter would have received 541 notifications!
To get rid of this, it would be great to see an "unsubscribe from notifications" button for commenters. Facebook have implemented a similar function and it works nicely.