I am an LEO from Florida and just returned from a vacation trip to NYC. I have never flown with a firearm in checked luggage. I found the experience to be easy, if you do your research and package your gun and ammunition according to the airline, TSA, and local laws. Flying out of Tampa was a snap. Not even a second look from the airline customer service rep. No law enforcement looked at my gun. TSA is on another floor, so I signed a single paper stating my gun was unloaded and they sent my bag off no problem.
Departing Kennedy was a slightly different story (with a happy ending). The ticket taker went bugged eyed when I said I was a police officer checking a firearm in my luggage. Because CCF is extremely restricted in NY, they don't have many people checking guns in bags. Port Authority Police and TSA were called to the ticket counter. The PA police officer was very polite. He checked my department ID and driver license. He briefly examined the gun, which was unloaded and secured with a cable lock. The gun, ammunition in original packaging, and empty magazines were placed in a small combination lock gunsafe in my soft sided suitcase. This suitcase was locked with a TSA padlock. The TSA officer looked through my bag and I locked it up. Process over.
The PA cop was very nice and escorted my wife and me to the TSA security checkpoint. He was going to jump us up in the line, but there was no line. Overall, I was extremely surprised at how helpful everyone was. I encourage you to carry off-duty (yeah, me and Dave Grossman) and not feel restricted by what might be perceived as a hassle, as I did.