To help bring this thread back to semblance close to the title... today I spent 20 minutes in immigration secondary at SJU.
I flew SXM-SJU this morning, and showed up early hoping to get on an earlier flight. I succeeded (yay!) and got on AA4887.
That was where the good news ended. One of the AA ground workers at SXM failed to add me to the manifest sent to Customs beforehand, and allowed me to fly anyway. As a result of this, I was questioned by immigrations about the purpose of my trip to SXM, my occupation, my income, if i have a girlfriend in SXM, etc. Finally they realize that I did nothing wrong, that it was the airlines fault, and they called for an AA representative. I got to witness them fine AA $10,000 for this and then I was on my way (hey, I'm a US citizen, they can't deny me entry).
Still though... if it weren't for the stupid requirement that all visitors even traveling to the US need to be essentially precleared first (even citizens), not to mention those merely traveling over US airspace, then this wouldn't have happened, and I would have been saved the embarrassment of being marched to a secondary room.