From BlenderWiki
Shrink/Fatten Along Normals
Mode: Edit mode
Hotkey: AltS
Menu: Mesh » Transform » Shrink/Fatten Along Normals
This is a advanced transform tool only available in Edit mode. It translates selected vertices/edges/faces along their own normals, which, on “standard normal meshes”, will shrink/fatten them.
This transform tool do not take into account pivot point nor transform orientation.