In the last 18 months I have spent more time out of the US than in it. CBP has probably slid my passport 15 or 20 times through their computers. What is on that screen they are looking at? I understand that there is a check for passport validity, and persons denied entry to the US.

Is there a list of dates of re-entry? The questions and inconsistency from officer to officer is why I am asking. On 13Mar2009, the officer really questioned everything he could about me, and I am a US citizen.

What was I bringing in? Nothing.
You didn't purchase anything to bring back? No.
Alcohol or Tobacco? No.
Countries Visited? Mexico.
Business or Personal? Business.
Who is your employer? Myself.
What is your position? Consultant.
What Industry? Manufacturing.
Manufacturing what? Repair parts for power plants.
What city in Mexico? Tampico.
What company in Mexico? __________ de RL de CV.
How long have you been in Mexico? 18 days.
Any other countries visited? No.
Are you sure no alcohol or tobacco? Yes, none.

Normally it is a couple simple questions, and then "Welcome home Mr. Lamarca, go on through."

You figure these people would see on the computer multiple entries into the US, from a US citizen, and it would not be a big deal. I flew out of Mexico into the US 3 times in one week, and didn't have half the questions this guy asked. That would have raised my suspicion.