Well... the maximize button continues every bit as useless as it was when introduced in System 5, IIRC.

But MacOS had some very interesting ideas - they did right more-than-one-user thing (copied from Windows) and Exposé.

Correct me if I'm wrong, but the "more than one user" thing is a Unix feature, OS X basically gets it for free. It's not copied from windows; if anything, windows tried to copy it from Unix, and it was horrible before WinXP

No. It's the desktop login thing. IIRC, you couldn't do that under X. Windows offered the lock screen and log-in as another user on XP. OSX decorated that with a 3D cube and Linuxes started getting it a couple years later.

While (I believe) you're right about Apple adding the 3D cube effect for multiple logins, X was explicitly designed to allow multiple concurrent users on the same machine. While many Linux distros did not have that configured by default in the early days, some did and it was certainly doable on the rest.

(That's one of the things that display managers like xdm/gdm/kdm do -- handle starting and stopping of X servers for user logins.)

But, if you stop the X server, what happens to the processes connected to it?