Stubby wrote:
I don't have a FAR/AIM here, but I do seem to remember there are a
number of exceptions that allow things such as ferrying planes, flying
around political candidates, and humanitarian work such as delivering
patients. Correct me if I'm wrong.

I think the following is the relevant regulation:

§ 61.113 Private pilot privileges and limitations: Pilot in command.

(a) Except as provided in paragraphs (b) through (g) of this section, no
person who holds a private pilot certificate may act as pilot in command
of an aircraft that is carrying passengers or property for compensation
or hire; nor may that person, for compensation or hire, act as pilot in
command of an aircraft.

(b) A private pilot may, for compensation or hire, act as pilot in
command of an aircraft in connection with any business or employment if:

(1) The flight is only incidental to that business or employment; and

(2) The aircraft does not carry passengers or property for compensation
or hire.

(c) A private pilot may not pay less than the pro rata share of the
operating expenses of a flight with passengers, provided the expenses
involve only fuel, oil, airport expenditures, or rental fees.

(d) A private pilot may act as pilot in command of an aircraft used in a
passenger-carrying airlift sponsored by a charitable organization
described in paragraph (d)(7) of this section, and for which the
passengers make a donation to the organization, when the following
requirements are met:

(1) The sponsor of the airlift notifies the FAA Flight Standards District
Office with jurisdiction over the area concerned at least 7 days before
the event and furnishes—

(i) A signed letter from the sponsor that shows the name of the sponsor,
the purpose of the charitable event, the date and time of the event, and
the location of the event; and

(ii) A photocopy of each pilot in command's pilot certificate, medical
certificate, and logbook entries that show the pilot is current in
accordance with §§61.56 and 61.57 of this part and has logged at least
200 hours of flight time.

(2) The flight is conducted from a public airport that is adequate for
the aircraft to be used, or from another airport that has been approved
by the FAA for the operation.

(3) No aerobatic or formation flights are conducted.

(4) Each aircraft used for the charitable event holds a standard
airworthiness certificate.

(5) Each aircraft used for the charitable event is airworthy and complies
with the applicable requirements of subpart E of part 91 of this chapter.

(6) Each flight for the charitable event is made during day VFR
conditions.

(7) The charitable organization is an organization identified as such by
the U.S. Department of Treasury.

(e) A private pilot may be reimbursed for aircraft operating expenses
that are directly related to search and location operations, provided the
expenses involve only fuel, oil, airport expenditures, or rental fees,
and the operation is sanctioned and under the direction and control of:

(1) A local, State, or Federal agency; or

(2) An organization that conducts search and location operations.

(f) A private pilot who is an aircraft salesman and who has at least 200
hours of logged flight time may demonstrate an aircraft in flight to a
prospective buyer.

(g) A private pilot who meets the requirements of §61.69 may act as a
pilot in command of an aircraft towing a glider or unpowered ultralight
vehicle.