Why the manual focus process is better on the Olympus E-P1 than on the Panasonic Lumix DMC-G1 – Brian Mosley:
Apart from the way you hold the camera, the main difference is the fact that the G1 cancels your MF assist zoom view the moment you half depress the shutter release button. We asked for this to be improved several months ago – with specific suggestions accepted as feedback by Panasonic – still waiting for an upgrade via firmware.
So, in summary, I personally find the E-P1 much easier in practical terms to shoot a lengthy series of manually focused shots… but the G1 could be improved any time now with a firmware fix (hopefully!).