I have a 2009 xtx, I would say between 14.5, 15.5mpg. That's cruising the UP with a very heavy thumb, I'am sure it could do better but it's just that fun of a motor.
I start getting nervous around 90 miles on a tank, if you plan ahead it's not a problem. Worse I got was 85 on a tank with one bar remaining but we were riding off trail in very wet heavy snow. With that being said next year I plan on adding the fuel caddies or extra can on the back.
Here's a link to TY with lot's of frequently asked questions, just click on real world fuel mileage.
http://www.ty4stroke.com/viewtopic.php?t=58910
Hope that helps, THINK SNOW!!!!!