i just installed the new I9000XWJFF firmware, and i really like it, i came from the custom firmware, but i think JFF is smoother. i havent redone the NAND mod yet, but i can say it feels like i am using it, things are alot faster. when i first flashed it, it gave me alot of trouble, swype was broken to the point it would crash going into anywhere i could enter text, so i had to reflash a second time, the second time i added CSC-I9000OXXJF9 to the CSC and that cleared everything up. so after an hour of use, i havent had any crashes or found any bugs, seems the fastest ROM yet.
EDIT: GPS lock in google maps seems faster to me, and the camera opens in about 1 second!
another edit: the wallpapers seem to be acting up for me, the phone shutting down randomly while the screen is turned off issue is still here