I have productively used, for significant amounts of time: every desktop Windows since 3.1, maybe a half-dozen Linux window managers under almost as many distros, BeOS, Solaris CDE, and more, a half-dozen GUI word processing programs, at least as many instant message programs, forums of all sorts, maybe a dozen image and WYSYWG HTML editors combined, and so on off to the horizon. I've figured out how to use obtuse UIs for games like Shadow President and Crusader Kings II.
Facebook's UI was too confusing so I stopped using it. I couldn't figure it out at all. Recently I've been exposed to "Facebook Work" or whatever, and it's just as bad. What's this? Where does this post go? To whom? Why are these in this order? Is this thing the same as that other thing with the same name, and if so why's it on the page twice and grouped with different things? WTF.