It depends what the overlap is of course. Something like music probably has a big age component in what people like for example.

But, yes, in general friends with at least reasonably similar preferences to myself are almost certainly a better source of recommendations for video, music, and books than a recommendation engine.

Do recommendation algorithms not take this into account already? Perhaps privacy policies make it harder to automate this effectively.

The famous ones may, but it ends up taking into account "what do we want you to see/listen/look at" much more into account.

The original Netflix prize also, it turned out, wasn't really implemented for a number of reasons. But one of them was apparently that Netflix doesn't necessarily want to give you the best recommendations; it wants you to keep your subscription. There's certainly some overlap between those objectives but they're not the same thing.

They're also incentivized to show you things that cost them "nothing" or "less" than others things - and if they KNOW the things you'd like to watch it's better for them to string those out so you keep subscribed.

The perfect Netflix customer is one always on the cusp of cancelling from lack of use but never actually does ...

In addition to the cost angle, they're also incentivized to push you towards exclusives. Things you can watch on other services (assuming you subscribe and know they're there) are much less of a hook to keep you on Netflix.

I have played ~5 seconds of one random episode from the front page on my Netflix profile since i subscribed around 2016. This was just to verify that it worked.

It still chuckles me up when they send me an e-mail once in a while, about what I might like based my past viewing preferences.

Note: My GF, has a profile that she uses sometimes, but mine haven't been used since the account was created.