As I have said before, the Gnome 3 Design and Development team has taken the decision to remove the maximize e minimize window button, but they haven’t announced yet if this deprecated functionality would be permanently disable or only hidden by default.

Yesterday, was posted in Diego’s Blog (one of the GNOME Project contributors) formalizing that the maximize and minimize window feature will be kept active and accessible through the window menu (right mouse click) or through conventional shortcuts, beyond the new gestures foreseen to the new Gnome 3.

Other detail, is possible to reactivate the minimize and maximize windows controllers using the "gsettings" (command line) or the Gconf_editor. In order to reactivate the buttons in Gnome 3 use the following line:

$ gconftool-2 -s -t string /desktop/gnome/shell/windows/button_layout ":minimize,maximize,close"

Using the Gconf-Editor, just go to desktop > gnome > shell and change the key "button_layout" to the value ":minimize,maximize,close", according to the screenshot below: