In Civil 3D 2011 there is more options to control what’s shown in Toolspace. You can turn off any of the available tabs individually. You can turn off/on the Prospector, Settings, Survey or Toolbox tabs. The toggles are available on the Home Ribbon. If you turn them all off the Toolspace will disappear. Occasionally the program will decide to hide one of the tabs, to get it to reappear you have to press the appropriate toggle twice to get it back.