Pilot-in-command question...

After looking online and in the FARs, I still can't see a definite answer
for the following question:

Let's say two pilots are flying together in an aircraft, and the aircraft
doesn't require more than one pilot and it's not a commercial aircraft. If
the pilots alternate flying the aircraft by handing off the controls to the
other person, do they also alternate pilot-in-command responsibilites?

The FAR/AIM defines PIC as: 1) has final authority and responsibility for
the operation and safety of the flight, 2) has been designated as pilot in
command before or during the flight.

Part 61.51(c) says a person can only log pilot-in-command time while being
"the sole manipulator of the controls."

Obviously it's OK to hand over PIC during the flight. It also seems that by
definition if you hand off the controls to the other person, whether you're
reading a map or taking a nap--you just handed over PIC responsibility and
you can't log that time. Things get a lot more complicated when the aircraft
requires more than one pilot, but I'm not talking about that and I'm not
talking about instructors either.

On a slightly different topic, is it legal by FAA standards to let a
passenger take the controls of an aircraft?

thanks, Tom Kreyche N21TK