Mark, When you do your preflight in the FMC, the TAKEOFF page does indeed provide you with the correct pitch trim setting. However, until you actually enable the autopilot during the initial climb, pitch trim is manually set. You're right, though...once the AP takes over, it handles pitch trim.

A question. I assume the FMC, once loaded take off parameters, should automatically calculate the trim. So, what do you mean by " properly trim the plane " if the FMC does it precisely ? Thx

It automatically calculates the takeoff trim, but does not set it. You still need to set it yourself, for instance, let's say that you got in the plane, and the last pilot left the trim at 4.0, When you enter takeoff parameters in the FMC, it calculates the trim, and displays 6.0. It's your job to set the trim to 6.0 before taking off

yep that's one of the rule of this big bird, trim is the key to mastering it whether it is manual or on automated flight, it's really important, as the plane is really reacting very quickly to subtle throttle input change, and things like that, that's something that will become even more important with the accuracy that seems to be at the heart of this aircraft.