Enable Infinite Scrolling, setting Diagram.scrollMode

          myDiagram.scrollMode = checked ? go.Diagram.InfiniteScroll : go.Diagram.DocumentScroll;

Enable Diagram.positionComputation function

          function positionfunc(diagram, pos) {
            var size = diagram.grid.gridCellSize;
            return new go.Point(
              Math.round(pos.x / size.width) * size.width,
              Math.round(pos.y / size.height) * size.height);
          }

Enable Diagram.scaleComputation function

          function scalefunc(diagram, scale) {
            var oldscale = diagram.scale;
            if (scale > oldscale) {
              return oldscale + 0.25;
            } else if (scale < oldscale) {
              return oldscale - 0.25;
            }
            return oldscale;
          }

This demonstrates new scrolling and scaling options available in GoJS 1.5.