Panasonic Bob (Steve's Digicam, Panasonic forum, 6 April 2004)...
Spot mode greatly reduces the area over which the camera calculates the proper focus setting. Let's say you are trying to shoot a closeup of a rose. You unknowingly place the `zone' in the middle of one rose petal. While the color is vibrant, that portion lacks any `detail' that the AF uses to focus. The end result may very well be a photo that is soft.
Now if you can use the center of the rose where there is detail, SPOT works to your advantage. I'm just trying to point out that it's very easy to accidently sample a detail free portion of any image (any solid colored object) and end up with soft focus.