Giving GNOME 3 a GNOME 2 Look
GNOME Shell Extensions have done more than any other set of features to make GNOME 3 usable. Nearly 270 in number, they provide a degree of customization that was missing in the first GNOME 3 releases. In fact, if you choose, you can use the extensions to go far beyond Classic GNOME and re-create almost exactly the look and feel of GNOME 2 while taking advantage of the latest GNOME 3 code.
The GNOME Shell Extensions site is more than a listing of options. It is also an interface for enabling and disabling extensions. To download and install an extension, go to its page and toggle on the switch in the upper left corner. In most cases, the extension is enabled without any need to reboot or to restart the X server. To disable an extension, toggle off the same switch.
If you forget which extensions you have installed—something that is easy to do—click Installed extensions in the main menu for a complete list, each with its toggle switch.