Just a few weeks ago, I caught an earlier flight from ORD to ATL after coming in from an international KE flight, and one of my bags missed that earlier flight.
Delta delivered it the next day for free, and I live 100 miles from ATL...actually they sent it to CSG and drove it about 30 miles up here. That was the scariest part - when they told me my bag was on an ASA flight
On a separate occasion, DL lost one of my dad's bags recently because they ripped the handle (and thus all the tags) off it...they did eventually find it after 5 days and sent the bag off to Delta's luggage repair shop (didn't know they had one). It came back with a handle, but not one of the same color as the bag. Oh well, it'll make it easier for him to identify it, assuming it stays on!
Delta has also sent my dad a brand new suitcase after banging up another one beyond repair. He doesn't have the best luck with his luggage, but at least DL always tries to make it right.