So in my anecdotal experience, I have been impressed with Delta in this regard.

In February I left my iPad in a seat back pocket. Didn't realize it until the next day, which was too late to get it back from the airport (I was told they send everything to the central lost and found in ATL if it is not claimed within 12-24 hours). I filled out the form online, and it took a little longer than I expected (about 1.5-2 weeks later), but they found it and sent me an email.

Last month my sig other left a neck pillow on board a flight back from AMS. They would not let us back on the plane, but an employee walked back to our seats and retrieved it.

And not quite the same thing, but yesterday during the boarding process, someone came onto the plane to give the woman in front of me her wallet, which she did not realize she left in the Sky Club. She barely muttered thank you. Fast forward about thirty minutes, when taxiing, we ran over something on the runway and damaged a tire, and had to go back to the gate for repairs. She was yelling at her bf/husband that Delta is the worst.

Regarding the post about turning everything into a third party vendor at the airport. I guess that is great if the item is found and turned into the airport where you last saw it. But in my situation, there is a chance the iPad was not found by the ground crew at my final destination. It could have been found a flight or two later, and how would I know that my airplane went to JFK and that is where it was turned in? I like the idea that items found on Delta planes go to Delta lost and found.