Filmmaking / Directing : The one about using facebook or other social media UI by Neo Bryce

I would check with them frankly. I would say yes but for licensing reasons, you may need to see if permission is going to be granted for that. Because Facebook and Twitter are brands like Pizza Hut or Pepsi.

Neo, with "fair use" copyright doctrine, you certainly can mention brand names, etc, as they are commonly known in real life. "Fair Use" allows limited use of copyrighted material without requiring permission from the rights holders, such as commentary, criticism, news reporting, research, teaching, parody, or scholarship. But where you can certainly get into legal trouble is with Trademark—using a registered trademark without permission.

On film, you can show some user interface that looks similar to the real thing, with minor changes, but not show any logos, brand names, etc. For example, notice how on sitcoms, TV series, or whatever, some character is using a laptop computer that looks just like an Apple computer (probably is) but there's no Apple icon or logo in sight. Or they're using some interface that looks like Facebook, perhaps it's blue in color, but again, no logo, no brand name or they just make up a fictitious name and/or brand. My favorite creative, side-step change to a registered trademark that I've seen is the Apple logo turned into a Pear. "Pear Computers." Lol! ;) Hope that helps!

Sure, why not! Write it. Let the producer worry about errors & omissions. Nobody sues the writer of a production

It's sort of a grey area.

It depends on roles, if you are just writing, go for it. If it ends up being made the producers will either obtain permission or design a look-alike so the audience gets it. If you are the producer, try to get permission or you could design a look-alike If you are the director and the producer couldn’t do either of the above, find a way to shoot around it!