Nice post over at revitstructureblog. A couple of highlights:
When working with Radial grids you will typically find a couple of problems. The first issue you will find is that the grids will not show on new levels. This is because the grids need to be elevated to cut through the levels and a grid is not shown unless a view is perpendicular to the grid as shown in the image below.
A new feature of Revit 2013 is the ability to create a continuous grid line with the same reference called a multi-segment grid. The grid is simply drawn with a series of lines and arcs and then when the sketch is finished the grid is created. It is worth noting that the grid cannot be controlled with a Scope Box (Covered Below).