Paramedics in PA have been able to do IOs for some years now. Maybe about 5 years ago we got IO drills that allow us to put them in adults. Before that we had to put them in by hand and that pretty much limited us to kids with their softer bones.
I've only done one IO, on an adult trauma patient. Very easy to do though it took a little psychological effort to get me to drill into someone's bone. In our protocol we administer some lidocaine first if the person in conscious because as I understand it, although the insertion of the IO isn't very painful, infusion through the IO is supposed to be very painful. As I said, my patient was unconscious so no first hand experience with that.