In 10.10 that I was using before 12.04, you could use Alt+F9 to minimize a window to the task bar.
In 12.04 Meta+Ctrl+↑/↓ maximizes and unmaximizes a window.
If you have a numeric keypad you can use Ctrl+Alt+0 to minimize to launcher.
On my netbook I don't have a numeric keypad and the normal numbers do not work with the above shortcut. How can I minimize windows with a keyboard shortcut?
I prefer the default bindings instead of needing customised ones:
This also happens to be the default in Microsoft Windows.
Unfortunately it's different for GNOME Shell. There you press:
Launch keyboard:
Shortcuts, windows, minimize window, click at the right of the bar as indicated
It will toggle to new accelerator. Just press CTL + ALT + 0 not the numpad zero.
Do note that the numpad zero shortcut will no longer work after you do this. Shortcuts now make a distinction between numpad numbers and across the top numbers, although it isn't noted as 'numpad0' in the keyboard wizard.
If your keyboard has 'windows' key, also known as 'Super' in Ubuntu, you can minimize, maximize, left-restore or right-restore using the key combinations:
If you wish to continue to use Alt+F9 then you can. For unity* just set to it in system settings > keyboard > shortcuts > windows as seen in the screenshot in aking1012's answer
For gnome-shell you need to set in gsettings, either graphically in dconf-editor as in screen or thru gsettings
gsettings set org.gnome.desktop.wm.keybindings minimize "['<Alt>F9']"
