This adds two modes to the 'around' drop down in 3d header

3d Cursor, only Ob Centers
Median Point, only Ob Centers

They prevent rotation/scaling from effecting the scale/rotation of the objects and just effects their position.
This is handy for aligning objects if you constrain to an axis and scale, as well as other neato things :)

Intrr came up with the code and I hacked it into the GUI

source/blender/src/editface.c

@@ -125,6 +125,7 @@ static void uv_calc_center_vector(float *result, Object *ob, Mesh *me)
 		}
 		VecMidf(result, min, max);
 		break;
+	case V3D_CURSOR_LOC:
 	case V3D_CURSOR: /*cursor center*/ 
 		cursx= give_cursor();
 		/* shift to objects world */
@@ -133,6 +134,7 @@ static void uv_calc_center_vector(float *result, Object *ob, Mesh *me)
 		result[2]= cursx[2]-ob->obmat[3][2];
 		break;
 	case V3D_LOCAL: /*object center*/
+	case V3D_CENTROID_LOC:
 	case V3D_CENTROID: /* multiple objects centers, only one object here*/
 	default:
 		result[0]= result[1]= result[2]= 0.0;