Like Brian, I use low ISO settings quite often to slow the motion of water, create an intentional blur, etc. I probably had 100-150 images in the last week at Lo -1.0 and only 1-2 test images at ISO 3200.
Normally camera companies like to report ISO in full stops - especially for base ISO. The D300 had better performance at Lo -0.3 than base ISO of ISO 200, but ISO 200 makes a nice round number for camera settings and specs - and there is little difference.
The color and dynamic range are much better at lower ISO levels. The performance is not quite linear - and varies by camera.
ISO levels are rarely exactly at the stated level - there is considerable variation. ISO 200 might really be ISO 187 when it is measured.