Bjorke, saying that the Planar 45 is sharper than the Summicron is a bit of a stretch. To me, all rangefinder lenses are sharper than SLR glass. They're both excellent performers!
Kate, the Contax G1 will always make a bit of noise and its focusing mechanism doesn't always allow for prefocusing. You can prefocus and shoot with any manual focus camera, but the Contax will prove to be a bit more difficult on account of its lenses always needing to move and to return to where they started. In Costa Rica, however, while the camera wasn't ideal for street shooting, it was an excellent travel tool, tough to take to the beach.
If you find the Contax focusing a bit slow... check the batteries before taking it out for a test. And welcome to the Contax G world!