I rented mine to a friend for a month. According to the AOPA Q&A folks
I talked to, no, the FAA does not consider it a commercial operation
becuase your buddy isn't "holding out" ie. advertising and offering to
rent it to anybody. It's considered just a deal between two buddies.

I had an insurance policy under AOPA that would allow such a thing, but
as posted here, it really depends upon who insures it. The policy
called it "limited rental," which again means that they recognized money
was changing hands but that this wasn't a comercial operation. It added
10% on to my insurance premiums which my friend covered as part of the deal.

On other thing. My insurance does have an "open pilot clause" and also
lets me add two other higher time pilots at no cost as also mentioned in
the posts. However, my insurance won't let people taking advantage of
these items pay for anything but fuel and oil. The "limited rental"
add-on is required for me to charge a maintenance fee.

Also, I've known of pilots who got around this insurance problem by
making a buddy a $1 owner of the plane. If you are listed as an owner,
you can fork in whatever amount of money you want in airplane upkeep
without any questions from the insurance folks.

Helen