Delta (DL) and Airbnb are now partners. They created a new website where you can log in with your Skymiles account and book Airbnb properties. www.deltaairbnb.com
You will receive 1 Skymile for every $ spend on booking Airbnb properties. Also, they are offering bonus miles for new costumers booking stays as well as new hosts (up to 25,000 bonus Skymlies for new hosts).
I have used Airbnb a couple of times and was very happy with the apartments I stayed. They were cheaper than a good centrally located hotel and it was a neat experience to live like a local for a few days.