First let me say that JKDefrag works great, and thanks for such a fine program.
After defragmentation is finished, I find myself restarting JkDefrag just so I can see the fragmentation map. I don't understand the point in blanking out the map, at the end, just to show the message "Finished". For me, it would be more useful to leave the map, and perhaps just put the finished message in a small box in the middle. Perhaps even better would be to just put the finished message in the status bar, or maybe put a two pixel colored outline around the map to emphasize that it's done.