Please don't take this as an expert opinion because its simply an opinion and I can't back it up by fact in any way...
I've heard that engine computers adjust to driving style. They "learn" how the driver operates the vehicle. Again, may just be a false rumor, but I've had a couple vehicles in the past that seemed to drive a little differently after having the battery disconnected for a while. The theory is that you reset the "learned driving style" in the ECU and let it start over.
The reason I bring it up is that most Jukes are test driven pretty hard. The drivers want to test out that turbo and feel the power, so they hammer them pretty good for the first 50 to 100 miles or more. Perhaps you did the same even after you bought the car. If so, and again, if the rumor is true, then the ECU may have learned to suit an aggressive driving style... one that is not so good on the fuel efficiency.
It couldn't hurt a bit to unplug the battery overnight and see if it resets a little bit. You'll just have to reprogram your radio stations
Once you've done that..drive it pretty conservatively for a tank of gas and see what you come up with for fuel mileage.