In my experience, the differences are very subtle unless the uprezzing is huge. I always considered Genuine Fractals to be a useful program for making poster size prints from small negatives and low rez sensors. The effects then are more noticeable. Certain edges in the image, around leaves, window frames, building outlines, rocks etc, appear sharp, although the detail within the objects is no better than bicubic can produce.
When the uprezzing with GF is taken to extremes, the image takes on a 'painterly' effect and you eventually arrive at something that begins to resemble an impressionistic painting.
