Ubuntu – Why does Ubuntu use two window managers: Compiz and Metacity

Compiz and Metacity are both window managers. You cannot use two different window managers at the same time. However, windows' decoration is done by a window decorator, not a window manager. You can use, e.g., either gtk-window-decorator (which can match your previous MetaCity themes), or Beryl's own emerald window decorator, which was made to work with Compiz, and has lots of nice themes.

Whatever you choose, be sure to check the settings for Compiz's Window Decorator plugin. (Run CompizConfig Settings Manager or ccsm and enable that plugin, and choose either gtk-window-decorator or emerald for the command; perhaps adding --replace if it helps.)

Running metacity --replace does not make it run as a daemon. If you hit Ctrl-C or otherwise stop that metacity process from running (closing terminal would do that as well), you will be left without a window manager. That is why you lose your window decorations. I am not exactly sure why the keyboard stops functioning (my guess is that once the window manager is closed new updates to the window, like typing, won't be painted to the screen), but I have tested this and if you hit Ctrl+Alt+F1 you can still drop to the framebuffer. Clearly the keyboard has not stopped working entirely, in fact if you click a menu item in gnome-terminal you can use the up and down arrows to navigate it.

You should run metacity in a wrapper, such as screen, when you need to start it from terminal and then close the terminal window you used. Just run screen metacity --replace and press Ctrl+A+D to detach from the screen process.