Mxsmanic wrote:

Yes, but I presume that outside of flight instruction, it's unusual to
put someone else in the left seat (especially if that someone is not a
pilot).

Actually, it's the comfort level of the pilot in flying from the
right side. Instructors spend almost all their time in the right
seat so they don't have any problems flying there. Most pilots
are inexperienced and extremely uncomfortable flying from the
right side. Of course, the other problem is that most of the
instruments are set up to be convenient for the left seat pilot
and as you go up in complexity you find that the right seat
controls sometimes aren't as complete. For example, in my
plane there are no brakes on the right side, so I wouldn't put
anybody but an experienced pilot in the left seat.

It looks like most aircraft have some things that are only accessible
from the left side, although I guess all the important stuff is
duplicated (?).

Actually, just the yoke and the rudder pedals in most planes. Most
light aircraft are small enough that you can see all the other
instruments from the right side. I actually got to fly in the
right seat of a Bonanza that had right side basic instruments
as well, but that's pretty uncommon.