The push notifications really resonates with me. Meetup.com is a good example of how to fail completely at notifications. Previously you were reminded about events you were attending and notified if someone messaged you. Both high value.
Now there are notifications for every event regardless of attendance, for every group of which I am a member. Also notifications for new groups in London — it’s a lot in a city this size. I tried setting my location to somewhere obscure just to reduce the load — but then when I did communicate with people they assumed I wasn't local undermining the social element.
So now I ignore all notifications, and have missed high value notifications. My use of the site has also dropped significantly as I’m not seeing what I need.
They are by no means alone, but it’s a case study on how to make a useful system completely ineffectual. FourSquare is another I’ll quickly mention. I missed that a friend was in the area and wanted to meet up as I stopped reading notifications like bob093030 has liked my tip about a sandwhich in the place I visited four years ago.