If you include Amazon book recommendations, I have to confess I have found those to be eerily accurate. Now I buy almost all my books through work, so I don't actually purchase from amazon much, but I still get useful recommendations by adding titles to my shopping cart that I end up buying through another vendor.

Regarding ads on the internet, I really see very few anymore. The ad-blocking and privacy options for browsers seem to be exceedingly good at their job, and I automatically switch to reader view for any page that enables it. These days I am surprised to see an ad online.