> As I understand it Wayland is _just_ a compositor.
Well, Wayland is a protocol. The application implementing the server side of this protocol is a Compositor. Current reference compositor is called Weston.
You can think of wayland compositor as X.Org and Compiz and Emerald and Gnome-Panel and XScreenSaver and a few more things all in a single application.
Wayland protocol is simple. It does not allow you to do most of the things you use daily. I.e. you can't have a dockbar or system tray, can't manage multiple monitors, can't even have a password-protected screensaver. Since none of these are supported by the protocol they'll have to be done by the compositor.
If wayland becomes popular you'll end up choosing between compositor with a nice taskbar, compositor with multiple monitors support and compositor with useful window manager.