I've been running
Ubuntu for a couple of weeks now.
Somewhere along the way, the application icon in the title bar of windows disappeared. This really bothered me. To get it back, here's what you need to do:
- Open "Configuration Editor" (Applications->System Tools or gconf-editor).
- Navigate down to /apps/metacity/general
- Set button_layout to "menu:minimize,maximize,close" -- mine was missing "menu:"