1. Racist memes, or seemingly innocent memes but with the logo of a known neo-nazi organisation on there. By reposting such memes, a person legitimises the organisation, and by proxy legitimises all their views. I got quite confrontational with my uncle about this fact, and he just didn't get it.
2. The fact that due to spam filters, unless you are friends on facebook with a person, if you message them there is no guarantee they will get your message as it will probably go into a spam folder which is no longer easy to access. Also they disabled the ability to poke someone you aren't friends with, so cannot get their attention that way. Some old friends have the friend request button disabled as well, I have tried messaging them, and I don't have their number.
3. Until recently the search used to bring up public posts from groups and individuals mentioning what or who you were searching for, which was very handy in various ways-for example alterting you to groups on that topic you were unaware of. Now the search just searches for members and a limited selection of public groups and pages, at least on my android app.