Magnified small central portion is KEY, and the only way to go if there is to be any semblance of speed in operation handheld (and any hope the G1 could be taken seriously as a digital RF). You must be able to see the whole frame while focusing. I wrote this the other day in the DPReview thread.
The method of getting there?- the Fn button's ok, but kind of hard to find with your thumb (I would try adding a glob of epoxy on it and hope it stuck, to differentiate it from the other 4way buttons). Since it's already assignable, that's likely the button w/ best chance for Pana to agree to adding a function on.
If the film mode button wasn't so flush w/the body, it could be a better choice- either control it w/your thumb, or use index finger, requiring a switch to using your middle finger on the shutter. For me it's still comfortable, and something I'd be willing to do to have a usable MF.
In either case, it would solve a poorly implemented half-feature currently on the G1. I bought it sight unseen, influenced by a lot of enthusiasm about how easy MF was. It's far from it. I didn't realize that they must have only tried it mounted on tripod.