Friendster, Hyves, Tumblr all struggled with their feed technology. Twitter and Facebook also struggled but at least managed to fix it. My first startup, Fashiolista, also struggled with the feed technology as we grew to millions of users.

On the flip side, it was that experience that prompted me to start Stream. We power feeds for over 500 million end users these days (https://getstream.io/). Kinda cool how nowadays you can buy a scalable version of pretty much all tech off the shelve. Algolia for Search, Stripe for payments, Twilio for voice, emails etc.