Q8: I'm a private pilot.  How should I log time in instrument conditions?

A:  The key concept here, and in most logging questions, is that the
    requirements for LOGGING pilot time (in FAR 61.51) are completely 
    distinct from the requirements for ACTING as pilot in command.

    If 
        (1) you are the sole manipulator of the controls, and
        (2) you have at least a private certificate for that category
            and class of aircraft
    then
        you may log the time as pilot in command.

    It does _not_ matter whether or not you are in visual or instrument
    conditions, nor whether or not you have a "high-performance" endorsement
    and are flying an retractable-gear airplane.  (If you are flying in IMC
    and are not instrument rated, you must have a current, instrument rated
    pilot who is rated to fly the aircraft in the plane with you. The
    instrument-rated pilot then _acts_ as pilot in command while you fly and
    log time as sole manipulator; the other pilot may also log the time spent
    in actual instrument conditions as pilot in command.)

    Much confusion stems from the long sentence in FAR 61.51(c)(2)(i) which
    governs who may log pilot-in-command flight time; this indented,
    specially punctuated "translation" of this clause should be helpful:

       (i)  A recreational, private, or commercial pilot may log as pilot in
            command time only that flight time during which that pilot
            (1)  is the sole manipulator of the controls of an aircraft
                 for which the pilot is rated, OR
            (2)  when the pilot is the sole occupant of the aircraft, OR,
            (3)  except for a recreational pilot, when acting as pilot in
                 command of an aircraft on which more than one pilot
                 is required under
                 (a)  the type certification of the aircraft, or
                 (b)  the regulations under which the flight is conducted.

    Instrument flight is much easier, as FAR 61.51(c)(4) shows:
    (4)     Instrument flight time. A pilot may log as instrument flight time
            only that time during which he operates the aircraft solely by
            reference to instruments, under actual or simulated instrument
            flight conditions. ...

    OK, so this means that
        (1) As a private pilot, you get to _log_ PIC whenever you are the
            sole manipulator of the controls of an aircraft for which you are
            rated.  Note that "rated" in this case means "rating", as in
            "airplane, single-engine land", _not_ "endorsement", as in
            "high-performance endorsement", or (worse yet) insurance-company
            endorsement.
        (2) If you're the sole occupant of an aircraft and you hold a
            private pilot license or better, even if you aren't rated for
            that category and class of aircraft, you can log it as pilot in
            command (i.e., you're soloing a glider as a student glider pilot).
        (3) As a pilot (doesn't matter what kind), you get to log instrument
            flight time whenever you "operate the aircraft solely by reference
            to instruments".