Well, jet pack is a misnomer. This is actually powered by a piston engine which drives two ducted fans. It is a little like taking the ducted fan UAV that Honeywell came up with (you can see a video of that here: http://machinedesign.com/Video/714/72766/HoneywellsHoveringUAV.aspx)
and upsizing it to fly a human. The demo was filmed at the recent experimental aircraft get-together at Oshkosh.