When my US passport is read by the airline counter/foreign customs,
what kind of information about me do they see?

Not sure how to select this for "answer", so I will post in comments.

When an airline reads your passport, they are able to see:
-All tombstone data from the passport (name, dob, pp#, etc.)
-Previous travel with their airline
-Booked travel with their airline
-Co-traveler information, if booked in groups.
-Checked luggage, credit card information (if reserved or paid ahead
of time), seat number, frequent flyer #'s

Additionally, Customs/Immigration (as well as seeing all of the above) can see:
-Previous enforcement actions against the individual
-Current lookouts on the individual
-Travel history irrespective of what airline was used (US/Canada
Customs can query back to the early 1990's)
-Cautions (i.e Violent, Armed and Dangerous, etc.)

If queried from an intelligence office, this information can be
processed further to include:
-Criminal history
-Employment, address, spousal, dependent information
-Shared travel history (i.e. contacting foreign countries to acquire
travel history in their country
-Conveyance information (every vehicle you've ever owned, licensing
history, infractions, etc.)
-Validation of passport and identification databanks
-Further intelligence from police or government agencies.

Hope this answers your question!

Cheers,
Michael

Just for your info, Michael,you can only select a question for
"Answer" if you are  a GA Researcher. I can tell that you're not
because your name isn't inderligned.

Mike, 

This is all very interesting and I would imagine that this is correct
without knowing for sure./ However, I am curious - how do you know all
of that (or is it a speculation)? Is there a document dealing with
this? Or have you worked at an airport?

I have a question regarding past travel history, if for example I
wanted to get information about how many times I've traveled and
where, would I be able to obtain that information at a Passport agency
or at another government agency?

HI Jennifermnyc.ga,
You will have to post your own question for that information  - if it
is available, which I doubt.