I ran the JF image on my G1 for a while and was pretty happy with it; only reason I stopped was it took him a while to do a UK Cupcake variant so I rolled my own rooted copy of that. While I haven't had to use the root functionality I figured I should take steps to keep it now in case Google decided to block it in the future.
So you had to root the phone before running the JF app right?.. did you follow a guide for rooting it?