I've had the bike for almost 5 years now, with just a hair over 52,000 miles on the clock, riding in just about any kind of conditions you can imagine. I've kept track of every fill up with a little app on my iPhone, and after 50,000 miles I dumped the numbers into a spreadsheet to create this chart.
The best mileage I ever got was 63.27 mpg (while riding along the Continental Divide, at low speed and high altitude), which would have given me a theoretical range of about 265 miles, or 426 km.
The worst I ever got was 36.30 mpg. I can't remember where that was, but I'm guessing it was somewhere out in the desert, riding into a fierce headwind with Caribou panniers mounted, and wringing the poor thing's neck. That tank would have only given me 152 mi./244 km.