The activity newsfeed hasn't been working since at least yesterday. My activities aren't showing up right away even though you can view them by looking at my profile. I'm not sure if the activities are being delayed or if they aren't showing up until the next activity is complete. In either case, right now my run from 2 hours ago still isn't on the feed.
On a related note, the widget that shows the recent activities for groups says that there isn't any recent activities to show, but if you click on the group name there are activities that could be shown.