For the United States, the relevant regulation is 14 CFR 61.51, which defines requirements for pilot logbook entries. In general, hours will be logged as one of the following categories:
- Training (i.e. Instruction Received)
Student pilots will log either as Training when flying with an instructor or as pilot-in-command when flying solo. Non-student pilots will log either pilot-in-command (when the Captain or the only pilot) or second-in-command (when acting as First Officer.) For purposes of total hours, all of the above are included.
Apart from the above categories, hours flown solo, in instrument flight conditions, and at night are tracked separately. These factors don't have any bearing on your total hours, but do matter for satisfying pilot certificate eligibility or currency requirements.Flight cycles (number of landings and takeoffs) don't matter in terms of total hours, but number of landings is also logged as a separate parameter.
14 CFR 61.51(e) says the following regarding what can be logged as pilot-in-command time:
(e) Logging pilot-in-command flight time. (1) A sport, recreational, private, commercial, or airline transport pilot may log pilot in command flight time for flights-
(i) When the pilot is the sole manipulator of the controls of an aircraft for which the pilot is rated, or has sport pilot privileges for that category and class of aircraft, if the aircraft class rating is appropriate;
(ii) When the pilot is the sole occupant in the aircraft;
(iii) When the pilot, except for a holder of a sport or recreational pilot certificate, acts as pilot in command of an aircraft for which more than one pilot is required under the type certification of the aircraft or the regulations under which the flight is conducted; or
(iv) When the pilot performs the duties of pilot in command while under the supervision of a qualified pilot in command
As far as whether rest time counts when operating long-haul flights, I wasn't able to find a definitive answer. The regulations in 14 CFR 61.51 don't seem to be terribly clear on that point. Even reading what actual pilots flying such flights have done seems to show that different pilots have handled it different ways with some logging all of the hours, some logging only when they were 'in the seat,' and others logging a given fraction of the flight time (e.g. logging 2/3 of the time on a 3-man crew where one rotates out to rest.) Perhaps one of our pilots with long-haul experience around here can provide more insight on this.
As far as the title question of how 'meaningful' the total hours are, that's a rather subjective question on which different people will have different opinions. Regarding your last question, certainly not every 1,000 hour pilot will have exactly equal experience, but how different their experience may be will vary quite a lot between any given set of two 1,000 hour pilots. It's entirely possible to be a 1,000 hour pilot without ever having sat in a powered airplane (by flying gliders, helicopters, etc.,) for instance.