When a new mesh is created, before it is selected or moved or anything, F6 can be clicked to call up a window which allows the mesh to be edited. However, I noticed that when I do this, all the controls are greyed out and I cannot edit the mesh. I am using Blender 2.73 RC1, but have noticed this occasionally in previous versions. Can anyone help?\
F6 is “Redo last action”. When you first add the mesh, the same options should be shown on the T panel (toggled on and off by the “T” key), so see if you can edit those. Basically, they are defaulting to some values that you are accepting, then trying to redo with F6.